It's more that when I see that effect, I have an uneasy feeling that a trigger could set things off the rails or shut off critical thinking or modify social standards for certain acts. I'm a bit of a contrarian at heart, so it's something of a non-specific mental immune response.

In fact, at (EU) football events, soccer hooligans are widely known for being violent. In the US, commercial and government propaganda are often dispensed in a socially validated environment. An alarming trigger (or a home-run that lands in the stands) can cause a stampede at stadia. I recognize that the more extreme examples are relatively rare occurrences, but they are more common than on say the street per square foot.

The irrationality of the crowd is something that unnerves me. I've been to games, so it's not like it's some paralyzing anxiety, but I feel some creepy crawlies at times.

Let me give you an example of a cohesive social situation that wouldn't creep me out: A town coming together for disaster recovery, where the people signaling cohesiveness are actually directly affected or are participating in the recovery effort. On the contrary, when people that are totally unaffected come together, it feels more uneasy to me because they are responding to a story being told on the news and are in a condition where simple manipulation is possible as they are not responding to advance their own interests (so certain sanity checks are disabled) and they do not have a good way to verify the story they heard.