It is entirely reasonable to limit the spectrum of playable characters to those who have some motivation to play the game with the other players. Stealing loot will reasonably upset the other players (not just the characters), by reducing the ways in which they can play the game. So no, it's not just creative freedom, it's being a dick. It's choosing to be a dick. GMs telling you not to do that aren't just limiting your creative freedom, they're telling you to stop being a dick or they'll stop playing with you.