How INhuman do you have to be to just stand there and watch it happen? This is one of those times where I think I wouldn't survive very long in the TWD world...it's tough picturing myself aligning with someone like Negan for protection.
Total fear. Rick is badass and he broke him to his will in one night, I'm guessing most of his gang was either in a group like Ricks at somepoint or have seen Negan do this enough that they're terrified of defying him.