The more I think about roleplaying, the more things I see that are just plain daft. A wonderful example is Dungeons & Dragons' alignment. The basic setup is that every entity in the world has an alignment, on two axes: law versus chaos, and good versus evil. This gives a range of nine possibilities, from lawful good to chaotic evil, with neutral as the middle on each axis. Now, if this was strictly a roleplaying thing, I'd have no issue with it; it's a two-word summary that helps you make snap decisions on how your character reacts to something. However, D&D takes it further: it becomes an actual thing. Your character has, permanently marked, his alignment. He's been branded Lawful Good, or similar. There are actual mechanical penalties for acting in a manner not consistent with that. This, to me, is ridiculous. Making a roleplaying decision, which may be entirely in-character, have a mechanical penalty makes no sense to me.
There is, also, the problem of alignment-based spells, from "detect evil" onwards. These also make little sense; they seem to be a workaround for a GM who can't make his characters well enough for them to be believably evil-but-seeming-good. Again, this is a problem of insufficient attention paid to keeping RP and mechanics separate.
This is one of the reasons I won't run D&D. I don't really want to play it, either. Please, don't get me started on class, either. I'll accept level, but really, you shouldn't be developing characters through mechanics if you can avoid it.