I am arguing with my D&D group about the following:
I, as a halfling rogue, want to play stealth, but some member of my group are arguing that I should play as a tank (which doesn't make any sense) just because I have a high Reflex.
My question is: should I still play hiding in the shadows and attacking over a distance to cause high damage or should I tank to protect the rest of my group?
PS: My party is formed by a paladin, a ranger, a wizard, a shaman, and me, a rogue.
Having a high reflex doesn't count for anything extraordinary. It's one of four defences beside armor, fortitude and will, and one quarter of attacks missing you more often doesn't make you a tank.
The magic of defenders, however, is not a matter of being unable to be hit. (In fact, they need to be hittable, so enemies don't give up and decide their time is better spent hitting the squishy wizard.) Defenders in D&D 4e take their denial abilities worlds beyond those of MC Hammer’s, and interpose themselves between their allies and anyone who wants to hit them.
Contrast to previous editions where what a class should be doing was up to the players to work out, D&D 4e introduced the concept of roles: each class has one role, which marks something they naturally do very well due to the powers and class features made available to them.
These roles usually suck at the other stuff (short of extreme optimisation), simply because they aren't given much to let them do it. An ordinary controller or striker won't be able to buff or heal their allies much, and a defender won't be hitting as hard as the striker.
Rogues are strikers, not defenders. They're not equipped with the stuff that makes someone good at defending.
Let's take the PHB1's classic defender—the Paladin—and see what makes them so suited for the role of defence compared to a rogue.
There’s a few statistical things: Paladins have better defences and armor, more health, and more healing surges, but these aren’t the key. They also get powers to heal allies and make everything harder for enemies to hit, but this is only a contributor to the ultimate power of what makes a defender a defender. (By contrast, the rogues just hit things harder, and get to move around the battlefield safely in order to hit other things and stay alive.)
This is the key thing defenders do better than anyone else. The key to defending is not being hard for the enemy to hit. Rather, it’s the interaction between the defender, their enemies and their allies which creates scenarios in which attacking the defender is the best option—but not a good option.
Defenders will usually not have ridiculously high defences, so that they're actually a reasonable target for the enemies to focus on. Being impossible to hit would be bad: the enemies would give up and find someone else to bludgeon! Defenders instead find other ways to stay alive, such as powerful self-healing. A Warden may have their health go up and down like a yo-yo between tanking and healing.
The Paladin has an at-will power called Divine Challenge, and they can keep it applied to any one enemy so long as they focus on that enemy. For as long as that enemy's Challenged, any time it attacks anyone but the paladin, it has a penalty to its attack and automatically takes a reliable chunk of damage.
Thus, the enemy could either pay attention to the Paladin whilst being lit on fire by the Wizard, or they could try to take down the Wizard, but be bad at it and get hurt in the attempt, in addition to the fact the Paladin's still beating on them.
The Fighter, the other PHB1 Defender, fulfils its role through mark punishment: an enemy attacking not-them receives attack penalties and invites retaliation from the fighter.
Fighters are specialists in close combat, and through target- and movement-denial, they’re the kings of lock-down. At level 1, a fighter with positional advantage can lock down a hallway by physically interposing himself between his enemies and allies. Anyone trying to shoulder past him gets stopped in their tracks.
BESW and trogdor, two of our regulars, together developed a build which combined the fighter's lock-down with its ability to push enemies around in order to lock creatures down way over there. It was frightening, and enemies targeted by this could do little more than cry in a corner until the party had dealt with everyone else.
Rogues don’t have punishment for attacking not-them. They can pick up a couple of specific abilities which grant it, but it’s not baked into the class enough for them to be effective at it consistently for long periods of time.
If a fighter stands next to you, you’ll either attack him or get rapidly beaten to a pulp by him. If a rogue stands next to you, you’ll get shanked equally whether you attack him or not, and he can’t do much about you attacking his friends instead of him.
Class roles should be used to their strengths, not fought against to try to fulfil a different role the class won't do very well anyway. Rogues have their strengths—they’re going to shank or poke arrows in people better than anyone else might—and as a rogue, you should exploit this strength as much as possible.
If your party needs a tank, they should look into getting themselves a defender.
Since Stealth is a skill available to everyone, there’s nothing forcing you to choose between stealth and defending: you can do both! There are builds available for defenders who want to be sneaky, too.
(And there's probably many more than that. If you're curious about BESW or trogdor's builds, find them in chat.)
You should play the character you want to play. If you want to be a stealthy archer, be a stealthy archer.
Even if your group believe they need someone to tank, rogues are strikers, not defenders. They gain a low amount of hit points per level and, more importantly, have no way to mark targets. Even if you had a rogue with arbitrarily high defenses, enemies could ignore them and kill softer party members first.
The paladin, on the other hand, is a defender. He has heavy armor, defensive skills and, most importantly, can mark enemies so they are punished for not attacking him. If anyone should tank, it should be him.
Your question is incorrect, as "stealth" and "tank" are not the right operationalizations of roles. They represent MMO jargon that if applied to its fullest extent, result in the characters being played against their strengths.
While it's seductive to import roles from other games into D&D, the cognitive shortcuts enabled by that jargon may make people miss important concepts.
In D&D, "stealth" is a "how". Specifically, it's a question of how the character expresses herself within the environment of combat.
In D&D, "tank" is an absolute trap of a term. Rogues have adequate defenses. They're not fantastic, but they're not a speedbump. The way the math works out, if a defender is engaging more than two or three people (depending on build) the defender dies. You're a (nominally) front-line melee fighter. There are two very squishy characters in your group, and the ranger may either be in combat with you (yay) or deciding to not pull her weight and firing a bow from the next county over. Either way, it's not the defender's job to defend you (most of the time.)
Everyone must pull their weight in combat. Overloading the shaman's capability for healing the paladin means that the group is less effective. The way the math works, it really helps things if there's a slight majority of melee characters (as a generalisation. If you're experienced enough to point out flaws in this due to specific party composition, this answer is not for you.)
So, be stealthy, use the stealth to engage enemies "in the rear." But you will be taking hits, and it's better for everyone if you do. Just make sure to try to take hits from, on average, one enemy at a time.
Ultimately, you should choose the path that suits the character and that you will enjoy. There is no reason in DnD4e that you need to fill specific 'roles' - groups of 4 strikers or 4 leaders or 4 tanks do perfectly fine.
If you want to be sneaky and in the shadows - by all means. Be sneaky and in the shadows.
That aside, a high Reflex is a really bad reason to do so, it is the least important defense. AC is targeted most, nasty conditions like stun and dominate usually come from Fort or Will attacks. Reflex attacks mostly just cause damage, and this becomes almost trivial after level 4 or 5.
It is a valid question however if you should work in melee, or with ranged attacks. This mostly comes down to party composition.
Melee: If the Ranger uses ranged attacks, your place is probably in the front line. The Paladin alone will not be able to lock down all the enemies trying to get to the squishies. Also gaining combat advantage is easier this way. Get a decent Melee Basic Attack.
Ranged: A melee Ranger and the Paladin are usually enough as a defensive line. And if the Wizard is a Close Blast specialist, you might even have a hard time getting adjacent to an enemy. Get the Distant Advantage feat.
Special situations might arise, once our party's tiefling Wizard was actually tanking the Big Bad Guy, as it was attacking Ref with fire, and had a fire aura too. Noone else would have lasted as long as the Wizard, but again, this was the exception, not the norm.
That said, do not build a generalist. If you try to be good at ranged and melee attacks as well, you will end up being bad at both.
TL;DR: almost never tank, but usually stay in the front line.
Mechanically, you aren't built to be a defender, no (and a tank, as has been pointed out before, probably isn't something any member of the team should be trying to be), but that isn't all there is to forming an effective party.
You mention in your question that the other members of your party want you to be a tank, and that you don't want to, and that this has led to argument within the party. It's important to the most D&D groups that the party works together as a team, and to all gaming groups that the players are not at eachother's throats. This is not to say that you should just give in to the rest of the group and make the character they want, especially since you actively don't want to be playing it; your character should be your own to create, and your discretion as to what kind of character you would like to make should have primacy. Nonetheless, good party-centered games don't have their characters made in a void: each player and the GM should give advice to all of the others and discuss how the group can best be made to work together and stay together. Suggesting that you make a 'tank' is a good and reasonable thing to do at a social level (though it makes no sense mechanically and is bad advice) in that it is an acceptable sort of suggestion to be giving other players during character creation. Arguing with you after you decided not to do it anyways, however, was not appropriate. You should figure out why your party wanted your rogue to be a tank and explain to them why you do not want to be one, but, and this is more important, you should discuss why the argument happened in the first place. You mention in your question that they wanted you to be a tank because of your high reflex score, but that would be (again, pretending the system works the way your party members think it does, which is wrong) a reason to advise that decision, not a reason for wanting that decision, and the fact that this turned into an argument indicated that they wanted you to be a tank. Reasonable people can disagree over mechanics and tactics without it coming to an argument. In discussing the argument you should make sure to decide with your group and your GM:
How much input the Party's other players should have on a member's character
How much input the GM should have on a player's character
How much desicion making power a player should have over their own character
Whether players are obligated to build the most powerful character they can or whether building a 'poor' character intentionally is ok.
How in-character inter-party-conflict should be dealt with
How out-of-character conflict can be avoided in the future
As a note, you don't always have to play a 'good' character (in terms of power level, I mean). A halfling barbarian or an orcish wizard are perfectly acceptable choices for roleplaying, you just must understand that you will not be very good at what you do. Sometimes struggling to overcome adversity can be fun, too. Even if it means being a halfling tank. The acceptance of this depends a lot on your playstyle and gaming group, though, so YMMV.
Even though you can have a super high AC through Dex and the right armor and magic, the lack of HP makes it difficult to say the least to take the punishment that the average tank is expected to withstand. Rogues are best suited as skirmishers, getting in, dealing a lot of damage, and getting out. Monks would fall into this role very easily as well.
