Because most people seem to believe in a single objective Reality™. It leads people to not just disagree, but to consider “the other” as having a totally broken thought process. Makes it a lot easier for people to dehumanize the other :/
A response of "Actually, it is the first day fall" I can understand, but how does observing that a given day is the first day of winter, to stick with the above, equate to having some kind of emotional bond with winter? I have never been able figure out the logical leap made. The only conclusion I have been able to come to is that the mere existence of certain keywords is enough to challenge their reality, and making it about the person helps them cope. But perhaps that is just me projecting the idea of a broken thought process on them.
Don’t make the mistake of assuming every account on the Internet is an actual human. I obviously have no way to prove such a thing, but it would be strange if there weren’t a massive amount of bots-posing-as-human online trying to influence opinions and behavior.
The greater issue we are facing is people unable to cope with "dissenting" (read: different) opinions because for whatever reason they think it's a personal affront on their identity for someone to disagree with something they've said online, under an anonymous (not for long!) moniker.
Facebook Isn't Other People. There is no 'democratization'. These platforms did not create anything. Facebook, Twitter, Gab, Parler, Win, Reddit, HN, Wikifarms, are fairly holistic in their representation of what people are actually like from the very beginning. You just don't want to admit you're as much of an asshole as the next poster, if you could get away with it.