I personally disagree, and think it should be allowed because you can simply choose to leave them the default class. If it's not in the game I can't choose to change their class anyway unless I can somehow cheat it in. This'll let people bring companions they actually like in their playthroughs, instead of bringing certain classes. Ex: Right now I want to bring Astarion along, but I want to play a rogue as well, so it's kind of sub-optimal to do so. As for it affecting their story or personality... you don't really need to be a warlock to make a deal with a demon (devil?), and wizards are just as capable of being abrasive as fighters.
