In my opinion, Bitcoin and Porn won't match each other due to the former's anonymity. Yes! Except legit and trustworthy sites like, Brazzers, Naughty America, etc. most other sites will turn out to be scammers and "ad-whores" since you can't claim anywhere that you bought an account there
On the contrary, it would be really helpful if the well-known sites start accepting BTC. But then again they won't do that, since there lies no proof that a 15 year old child is buying an account! That's why credit cards are a must for legitimate sites!
Accepting porn-related altcoins like: titcoin, sexcoin, etc. would have been nice but those coins should never be made anonymous for the above mentioned vulnerability!
And if you are really interested in watching free, moderate quality porn vids, then you already know where to look out for