4chan (and it's successor 8chan) mix two tendencies. One is to post horrible or strange things for the sake of it. The other is to post things that have some validity or purpose, but would be censored in other places. Now clearly what things one puts in what categories are very subjective, but there are certainly people who claim to belong largely to one or the other group (as well as neither). But so far there hasn't been an approach to allow the second category but not the first, so people who have views that don't fit into the mainstream (mostly on the political right) tend to congregate at this sort of place.