Supposedly Spez was made a mod of that subreddit by a troll who exploited a bug/feature that allowed you to make anyone a mod of your subreddit. However reddit did host that community for years (Spez claimed the creep mods were helpful in flagging cp throughout the site), and it's ironic you mention "problematic" communities migrating to 4chan in the same context, since 4chan takes a much harsher stance on the sexualization of minors than reddit. KiwiFarms even more so.
> You really don't want reddit users here
No one wants reddit users.