Reddit always had an element of \dchan in it ever since user subs were created. Coontown (and the preceding slur subreddit), FPH etc.

In my view this is just a symptom of the wider populace gaining access to internet forums and the cultural shift mass internet usage brought. As in, there have always been darker corners of the internet, just that the people who frequented them had to have some level of nerdiness/geekiness and {nerds}∩{violent racists} is smaller than {whole population}∩{violent racists}.