There was a real technical or situational hurdle to even be present on the net back then, and I think most users had a sense of wonder and perhaps respect for the platform they were privileged to even get a glimpse into and partake in. Maybe? Today the amount of low-effort/low-value thoughtless vitriol makes up a much much larger percentage of the communication and web content than "back in the day". Spend but a few moments and you will encounter some flamebait/sensationalistic noise. It used to be a lot harder to be subjected to such stuff. Tragedy of the internet commons, or something.
Thus you would remember a bit of the tail end of the era before Eternal September.
Normally, September was the time when a crop of new students would get accounts at universities and step into the world of Usenet for the first time, behaving like asses.
In September 1993, AOL connected to Usenet. That became known as Eternal September.
https://en.wikipedia.org/wiki/Eternal_September
The online world we have today is basically the continuation of Eternal September, reaching further depths of deterioration.
I'd suggest you missed noticing some of the more divided corners of Usenet back then. Consider (admittedly an extreme example)
https://groups.google.com/forum/#!searchin/soc.culture.yugos...
The real problem with practically every internet community is its moderation, because the worst people with the least business doing that job inevitably float to the top and are then impossible to dislodge without voting with your feet and creating an entire new community.
It's overly reductionist to attribute Trump and Brexit just to online trolls, but it's folly to ignore their effect at the margins (because both Trump and Brexit were relatively close calls, influencing a 5% middle ground definitely mattered).
A good portion of the ragamuffins who are overflowing the online world have not such concept. Everything is personal.
Though in some ways it's the same, here is the difference: it has become more diverse.
In 1991, the people you might have conversed with on Usenet were a lot similar to you. Of course, if we go to some comp.lang.* newsgroup or whatever, people are similar even today.
But I mean that if you went into any newsgroup whatsoever in 1991, on any topic, everyone there would probably have been some sort of professional in a STEM field, academic or university student. Go to, say, rec.pets.dogs, and it wasn't just any dog lovers from any walk of life, but mostly engineers, programmers and sysadmins who are into dogs.
That's way different from going into Reddit today, where it's now any Tom, Dick and Harry from any walk of life, who only have a certain topic of interest in common and that's it.
People have social interactions online which they wouldn't have in real life. In real life, if you run into someone who is from, say, a "lower" social class, they have it written all over them, and it puts them in their place more effectively than any downvoting system.
For instance, in real life, you would either never argue politics with an obvious "despicable", or else you'd immediately attribute everything they say to the limited scope of their background and just nod your head politely.
Basically, there is no new divisiveness; the quiet divisiveness we already have just comes out when people get together and hide behind aliases and avatars.