There seems to be several issues.
- Many image hosts don't want to host adult content at all, as they think it's going to reflect badly on them.
- Many image hosts want to force adverts and thus require an account to host images.
- Many image hosts are afraid of finding images posted on their site that are illegal, were legal when originally posted but now are not due to changes in the law, or where it's not clear if the image is legal.
All of these are probably part of
imgur's decision.
In the latter case, as we have seen, the last point is particularly important for forums, whether self-hosted or not. Even if a forum can find a hosting company that allows 'adult' images, the forum must still police itself, especially from images whose legality changes over time due to changes in the Law (or how the Law is interpreted); it can be unclear whether a specific image is legal, due to poor wording of the Law and the ease in which the Law can be flexibly interpreted, especially when challenging something in Court takes ages and costs a fortune even if you win, as Phil has found out.
As long as MLDC has a host that allows 'adult' images and is well moderated we ought to be OK.