I wrote two sensitive articles here on HubPages. One was about America's Fear of Sex and Nudity, and the other was about Art versus Pornography. Because of the words I used, the ads were automatically disabled. However, this only applied to google ads, not amazon ads, which are placed by me. Generally speaking, if you approach sex from an education/analytical side, then you are probably okay to post it, but just don't expect to make any money off of it. If you're writing erotica fiction, there is a good chance the hub will get removed. The same is true if you use explicit photos.