Well it is possible not to spend the cash and pay in bitcoin.
Credit Cards is not cash.
Really. Mostly if porn site is not free as usually you are paying with card there. So you just can cash out your bitcoins on your credit card and pay what ever you wish. Every day it stay fewer and fewer places that accept only cash.
Well for me it credit card is just a real cash for me because i can use it here in my country like eating in fast food and give my credit card. that can help just not use your pocket money if you are in outside.. also here in my country we will have a good credit card that actually you can deposit only with bitcoin..