I disagree that they can't have it both ways, because I don't see the contradiction that you are implying here. Often when people talk about "no evil PCs," it's really about the social contract of play: The Will Wheaton Rule, i.e., "don't be a dick." It's less about alignment and more often about disruptive players who ruin the fun of others or wanting to preserve the heroic tone of the game rather than the alignment itself. Even the whole "that's what my character would do," regardless of that player character's alignment, should not be an excuse for the player's "Wang Rod" behavior that negatively affects the fun for other players at the table. I would never use alignment as a rod to tell players how their play is affecting others or disrupting the game. That's a conversation that I would have with the player as an individual rather than try to enforce through alignment. I think that it's useful to recognize the open, respectful conversations that should happen between individuals.