There is a adult content on the relays but it is filtered by clients. If you search for the right hashtags you’ll find it in most clients. On slidestr I filter by content warning, hashtags and some „known npubs“ - that works surprisingly well. It needs some manual maintenance though. 

 It's the illegal non-adult stuff I'm mostly worried about. I want to run my own node, but I'm in the process of considering the possible legal implications of doing so. Lots to learn. Thanks!