It's called being a decent human being, and if you're not doing it, then you are no longer "innocent" or the proverbial "nice guy" either. No, you're not responsible for every single interaction around you. Yes, you are responsible for keeping your friends in line when they're doing something stupid or wrong. (That's what friends are for, as the song goes.)
I have dropped friends who were total asshats and refused to listen to my advice on how to stop being total asshats. I can only hope that if enough of their remaining friends drop them for being asshats, they eventually get a clue and stop it.