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.