A while ago, I ran into an interesting conflict in a game that got me thinking.
I was playing in a party with a Knight/Paladin and three other characters. The Paladin was playing what essentially amounted to a wandering freelance cop, bringing justice wherever they found injustice, while the rest of the party was following along for the promise of gold rewards. Everyone, players and DM, was happy with this arrangement, as it brought regular sandbox style quests and good money.
The problem began when we ran into a deliberately grey moral situation presented by the DM. A drow entered a human village and was immediately captured and thrown in holding before public execution. The party discovered the drow was a thief, and the Paladin wished for the drow to be brought to proper justice for this, without the extreme of hanging "because drow". The paladin makes a deal with the drow: they'll free him from execution if he surrenders to whatever local laws did to thieves. Drow agrees, paladin convinces local law, drow pleads innocent of all charges, local law lets him go due to lack of evidence. Paladin is upset.
Up until now, the rest of the party has been with the Paladin, helping in endeavors and generally agreeing with the course of action. This changes when the Paladin decides to go after the drow, talking about capturing him and hauling him off to the "Drow Town he came from" for whatever justice they choose (Paladin is in character not knowing how drow or their cities work). The rest of the party protests, saying it's probably several weeks' journey, but the Paladin is dead set and will not be convinced. Eventually the party begrudgingly agrees to follow, they catch up to the drow who resists arrest, and they mostly-accidentally kill him. It's bittersweet, but everyone is more or less okay with this resolution.
After the session, the player of the paladin explained the behavior sort of like this:
My character's major arc and theme is that he believes justice is a black and white, simple thing that he can recognise and deal with. In reality, justice rarely is, and I appreciate being given a situation that allowed us to explore that. My plan for the character is for him to slowly realise this complexity, and rely more and more on the wisdom of Bahamut to tell him what to do. I'll figure out how to take his development from there when we get there.
Where is the line between roleplaying a naive, stubborn character undergoing development and being a problem player? How can we portray internal character conflict and personal flaws without ending up in "My Guy"?
Clearly there are instances in which playing a flaw or ignorance like this is acceptable, otherwise we would all be playing Mary-Sue characters.