It’s not like the circumstances of the experiment are significant to the subjects. You’re a college student getting paid $20 to answer questions for an hour. Your response has no bearing on your pay. Who cares what you say?
That would fall under the "discernible reason" part. I think most of us can intuit why someone would follow the group.
That said, I was originally thinking more about soul-crushing customer-is-always-right service job situations, as opposed to a dogmatic conspiracy of in-group pressure.
To defend the humans here, I could see myself thinking
"Crap, if I don't say 1+1=3, these other humans will beat me up. I better lie to conform, and at the first opportunity I'm out of here"
So it is hard to conclude from the Asch experiment that the person who says 1+1=3 actually believes 1+1=3 or sees temporary conformity as an escape route.
Look up the Asch conformity experiment [1]. Quite a few people will actually give in to "1+1=3" if all the other people in the room say so.
It's not exactly the same as LLM hallucinations, but humans aren't completely immune to this phenomenon.
[1] https://en.wikipedia.org/wiki/Asch_conformity_experiments#Me...