I don't see the problem here.
Guys do you seriously believe that anyone would sacrifice themselves by creating something like pirate bay without any personal return?
Remember: if it's free it's that you're the product.
You can pay every film and game you dowload illegally on something like pirate bay
Or you can chose to give them parts of your CPU power to mine btc and pay them like this.
Easy choice for me!

Lol - true - I guess in this instance ethics isn't a major concern - either for the users or owners. Outside of the pirate bay though - what if you were paying for a Netflix subscription and they were stealing cycles from your CPU in a way that you would never know - would you care?