New Vegas is a fascinating game to me because it lets human instinct do the work of deciding whether the asshole faction is good or bad.
Most games tend to route you into exploring the antagonists by doing one or two mandatory introductory missions for them, or using equivocating narrative. New Vegas doesn't really do that. You're free to interact with them but also you're instinctively repelled.
When the game introduces you to Vulpes, you're free to smoke him then and there. Legion hit squads will come after you and make the game much more difficult at that level, but you can survive. Typically, a game wouldn't make that possible. It would introduce him and make you interact with him a little before maybe some sort of miniboss fight if you so choose.
@Zero_Democracy It's what I like about New Vegas. Very few characters are marked as "unkillable" even temporarily. You can murder-hobo your way across the mojave and still finish the game with your 67th Yes-Man at your side.
