When I was in the military (yeah, military service is mandatory here in Finland), at one point there appeared in our barracks a box for making suggestions. I got an idea: The rooms didn't have mirrors in them. I thought that mirrors could be great, especially since we often had to put on ties for special occasions, and so on and so forth.
When I presented this idea to the other guys (there were something like 12 of us in total), to my complete puzzlement every one of them disagreed, and not a single one of them could give any rational reason why. They just disagreed, period. To this day I don't have the faintest idea why. I don't even have a layman's hypothesis of the psychology behind it. There would have been zero drawbacks in us having a mirror in the room (and if there had been, they would have certainly used it), yet they all disagreed, and couldn't give a single reason why. They just did, period. Thus we got no mirrors.
This isn't a unique case. Of course it's not tremendously frequent, but it does happen from time to time. Nowadays online it happens quite a lot.
EEVblog is a YouTube channel that publishes frequently videos about electronics. One common video series of the channel consists of "teardown" videos, where the host opens an electronic device and examines its interiors. The motto of this series is "don't turn it on, tear it apart".
He doesn't always follow that principle, and he occasionally does turn the device on before tearing it apart, but oftentimes he does not. In one video in particular I would have been interested in seeing the device in action, before he opened it. I made the suggestion that to make the videos more beginner-friendly and watchable, he could spend something like a half minute simply briefly showing the device in action, ie. what it does and what it looks like when it's on and is used. (This particular device, which was some kind of multimeter, had a display, so it would have been interesting to see what the display looked like when turned on, and what kind of things it would display and how.) Since the video itself was something like over half hour long, adding half a minute to it wouldn't have made it any significantly longer, but it would have made it more interesting.
Well, you guessed it. Almost every single person who responded to my suggestion disagreed. None of them could give a good reason why. (To be fair, in this case I got a couple of agreeing comments. However, they were inundated by dozens and dozens of disagreeing ones.) The thing is, if the original video had had that kind of short segment showcasing the device, I'm completely certain that nobody would have criticized it for that, but on the contrary would have liked it. (In fact, I'm certain that if then somebody had criticized the video for that, these same people who disagreed with me would have defended the video.) Even when I pointed this out, they wouldn't budge.
These are by far not the only examples that I have experienced, but I think they are illustrative. Sometimes, for some strange and random reason, lots and lots of people just disagree as a group, even when not one of them can present an actual good reason why. (It would be quite different if some people disagreed, while others agreed. That's normal. It's strange that sometimes all of them seem to get this strange urge to disagree for no good reason.) And it's quite random; you can never predict when this will happen.