So there's a thing called the "waiting room experiment." You can watch the first 1:30 of the video and get the idea. (Short version: if you put a subject in a waiting room with a bunch of experimental participants, and then sound a bell repeatedly, and they all stand up and sit down on the bell, the subject will eventually start doing it, too.)
A friend shared the concept with me (I dug up the video myself) and said that this was a bad thing. I think that "Humans are stupid" was the term. And my impression is a lot of people feel similarly: people are sheep, they're mindless, they don't think for themselves. Something like that.
But I thought about it, and I wonder: maybe this social conformity can have some really powerful upsides, as well. If you're in a new and unfamiliar situation, consider: if everyone's doing something a certain way, there might be a reason for it. You might not know the reason, but hey! Those people all look pretty healthy and calm with their standing-up-and-down, and it won't hurt, so why not? Maybe it'll just make them happy, and that's good enough for me!
Of course there may be a downside to this part of our brain. It may discourage innovation, or challenging tribal wisdom or conventional norms. It may slow change. But it may also reduce chaos. It may keep us from making some really bone-headed mistakes before we've had the opportunity to think everything through.
But I remember a conversation with my grandmother in which I was defending some action or another:
"My friends are all doing it."
"If your friends all jumped off a cliff, would you?"
"...I mean, probably. Seems like if they're all bent on it, it's a good idea."
She didn't like that. But it's something to consider.