Look, I will give you just one example. Look at the mess with the Ashley Madison. Imagine if their users had an opportunity to pay in Bitcoin by staying anonymous or even semi-anonymous. I am sure many of them would choose this option.
Bitcoin can have many use cases like this one in the adult and porn industry, meeting and dating websites, etc. And I am sure it will have after the Ashley hack.
Paying with bitconis on a cheating site and waiting for the site get hacked and your identity connected with your bitcon address(es) would be terrible. So not only these people could be identified as cheaters, but also you could view their balances on addresses, chceck who's reach, whos not, etc. If you want to use bitcoin for something, please remember that bitcoin is not anonymous (
http://www.bitcoinisnotanonymous.com/).