The problem is that 1) they radicalize each other and reinforce their worldview about how non-white people, women, homosexuals, lower class social groups, etc. 2) they coordinate and plan their harassment campaigns and focus their efforts on specific targets 3) they hype each other up and create lies to justify online terrorism of marginalized people
And what is stopping them from doing that now? What ever WOULD stop them?
Stormfront and the many ties that bind it to myriad other sites still exists -- and if it didn't, something else will take its place. It's human nature to seek others who think the same. They will ALWAYS congregate in their respective churches, they will ALWAYS plan harassment campaigns, they'll ALWAYS reinforce their worldview. There is absolutely nothing you can do to stop them from doing so.
But we can still marginalize their sincerely held, fucked up beyond repair, beliefs when they deign to step outside of their echo chambers.
They excel on 4chan because of a relative lack of moderation, worsening -- as they are wont to do -- when moot simply stopped bringing new moderators on board before he left. /pol/ and its predecessors used to get deleted, reintroduced, and moderated stricter, but there is only a LOOSE community, where anyone can simply join the conversation...or leave the conversation. Moderators and janitors on 4chan in general don't last very long. Threads are constantly moving, so it's a Sisyphean task to control more than a few at a time. Then, while we may be able to drop drive-by comments, derision doesn't last long. Years of derision for even the simplest of things dulls people to it. Instantly recognized as a drive-by comment, it gets ignored, perhaps even hidden to remove clutter, and the cacophony continues on.
They excel on Reddit because there are far too many people for the small number of moderators per subreddit, so more offensive subreddits leak. For the more offensive subreddits, it's easier to curate content and comment alike, as they won't have to deal with the general public. While downvotes tend to curate comments, no amount of bandwagoning downvotes will keep those people off the boards, only more moderation -- they'll be able to scurry back home to their toxic environs and collect upvotes for their offensiveness there.
They excel on Twitter because of the ease of making an account and again, relative lack of moderation, with anonymity. Even when they ARE banned, they make a new account. Even when they are blocked, they can use another account. If they are planning at all, it's not likely able to be traced back to them, anyway.
But then we have a place like Neogaf -- a waiting period to join the site, clear and concise rules, moderation in spades, with moderators who are not afraid to use the so-called nuclear option of banning people, locking, and removing threads. Even here, though, you have people peddling their toxic ideologies for a little bit before they are banned. Sometimes they'll even wait it out until they're a member and then do it. Sometimes they'll come just up to the line and not cross it, and the moderators probably watch them carefully.
The rules don't really matter -- they feel they are beyond rules. Only the consequence matters.
They face no consequences in a world with proxies, dynamic IPs, anonymity. You could ban proxies and IP range ban, you could implement some sort of identification requirement(although this can lead to its own problems), but doing so will put other people out. Innocent people or, at the very least, not guilty people. And sure, it's easy to punch holes in that, making exceptions for those people, until the people you want to keep out worm their way through there, too.
It's a constant battle to control their ideologies, and keeping it contained and monitored is really the best we can do, from my point of view. Otherwise, we wouldn't have this problem in the first place!