As you allude to, this is a very straightforward phenomenon. The founding population of the Internet is not identical in distribution to the population that now exists on it. Most people are small and vicious and incredibly stupid, and now the population of the Internet[1] looks more like "most people" than it did in its early days.
There's practically nothing to see here. If a bunch of chimpanzees join a club, it's not that interesting to note that there's suddenly shit being flung everywhere.
EDIT: just to be 3000% clear, given the current obsession with the topic, my comment and use of "chimps" has less than nothing to do with race. It's a reference to our entire species' primate past and the tendency to underestimate our similarity to those ancestors.
[1] Limit this to the developed world if you'd like. Countries that came online much more rapidly and recently, and continue to have large portions of the population come online every day, are dealing with a different but related set of problems.