Never. Piracy is theft. Simple as that, no matter how anyone wants to justify it. Need proof? I am implore anyone to put themselves in a position where you are the one spending your time , money and talent to make something that cost you a lot to make, then tell me under which circumstances you would be OK with people just copying and sharing your hard work.
Having said that, like most people here, I'm a thief. I don't pirate games though, cause I feel their actual sale is the only way they make their money.