I'm trying to create a race for Pathfinder and decided to give them an at-will spell-like ability. Now, it says that you cannot choose a spell that deals damage, but would a healing spell count as a spell that does damage? Now, some healing spell don't directly do damage to most things, but could be used against undead foes to deal damage.
Yes, it does.
I believe we are talking about the Monstrous Traits racial trait.
Monstrous Traits (Magical)
Spell-Like Ability, At-Will (Variable, see Special)
Prerequisites: None. Benefit: Choose a 3rd-level or lower spell that does not attack a creature or deal damage. Members of this race can use this spell as an at-will spell-like ability. The caster level of the spell is equal to the user's character level. Special: This trait costs as many RP as twice the level of spell chosen (minimum 2). Up to five spells can be chosen when you take this trait. Each time you take an additional spell, adjust the RP cost of this trait appropriately.
So, we have to consider that Cure Wounds spells are Touch spells, though if the target is willing, no check is necessary.
That they also have a Saving Throw:
Saving Throw Will half (harmless); see text;
And the spell effect clearly states that the spell applies positive energy to the target, so a target that is harmed by positive energy, such as an undead, but not limited to them (Damphir, Death Domain Clerics, eidolons with Undead Appearance, Bone Mystery Oracles, or Agents of the Grave), will take damage instead of being healed.
You must touch a creature or object to affect it. A touch spell that deals damage can score a critical hit just as a weapon can. A touch spell threatens a critical hit on a natural roll of 20 and deals double damage on a successful critical hit. Some touch spells allow you to touch multiple targets. You can touch up to 6 willing targets as part of the casting, but all targets of the spell must be touched in the same round that you finish casting the spell. If the spell allows you to touch targets over multiple rounds, touching 6 creatures is a full-round action.
And finally, the harmless saving throw means that the creature can resist the effect if it doesn't want to be a target, or doesn't know what spell is being cast and doesn't trust the caster, or simply can be damaged by positive energy and wants to resist it.
The spell is usually beneficial, not harmful, but a targeted creature can attempt a saving throw if it desires.
You will notice that the header of a Cure spells is absolutely no different from other touch attack spells, except for the spell effect. On the Magic chapter, we get the definition of spell attacks:
Some spell descriptions refer to attacking. All offensive combat actions, even those that don't damage opponents, are considered attacks. Attempts to channel energy count as attacks if it would harm any creatures in the area. All spells that opponents resist with saving throws, that deal damage, or that otherwise harm or hamper subjects are attacks. Spells that summon monsters or other allies are not attacks because the spells themselves don't harm anyone.
For all purposes, the Cure Wounds spells are considered attack spells that cannot harm creatures that are healed by positive energy and will, instead, heal them. The same way a target that is healed by negative energy can accept an Inflict Wounds spells, or one that is healed by fire damage can willingly fail a saving throw to resist a fireball, and so on.
What's happening here is you're asking us to issue a house-rule for you. We can't do that! We're not your DM.
From a very strict Rules As Written perspective, a spell is an attack if you can make a saving throw against it, and that's true of basically anything that you can use on another creature. So, yes, a cure spell does technically count as an attack.
If you went and asked your DM about this, you'd have an interesting case. On the one hand, obviously a cure spell isn't actually an attack, and most sane DMs should be willing to handwave that rule for you. (You could probably agree on a variant of cure that can't be used to damage undead.) On the other hand, you're trying to create a race that has infinite at-will healing, and your DM might feel that was overpowered.
The race creation rules are intended to be used by the DM, or by players with DM oversight. You're going to need to get DM approval for your race no matter what you do, so you may as well start by asking for it now. :) If you are the DM, remember you can apply Rule 0.