With regards to porn, many would argue it does harm others by messing with your sense of adult sexuality/proper sexual interaction with others.

Plus just look at Jersey Shore every time one of those blockheads has sex there's another cryfest the next morning. Clearly it makes everyone on your block's hangover worse by enducing shrieking sobs of remorse and confusion.

tl;dr sex kills kittens don't have it!!!!!!!