I disagree again. You don't have to be a douchebag that posts vile things to believe that the free speech slippery slope argument may be merited.
It's relatively easy to either only remove illegal content or to have very strict moderation (ala Facebook). It's much harder to only remove certain kinds of "offensive material" without removing too much.
But the banned subreddits had nothing to do with the content on them. This was not even remotely about "offensive material". This was purely about the subreddits engaging in campaigns of harassment against other people. That's not a free speech issue in the slightest. There's no slippery slope here. The only people who should be upset about this are either people who don't understand what happened (which seems to apply to you), or people who think they are entitled to harass other people online without being punished (which is, sadly, a very large number of people on Reddit).
This is the first I've heard of there being explicit rules and measures on the replacement subs. My understanding is that they were banned because they represented an attempt at ban evasion (which is itself a serious violation of reddit policy and always has been), but I admit I haven't done much research on the replacement subs because I didn't think it was particularly important.