That quote is pirate propaganda.

1) All of the heavy lifting is done sneakily by the word "purchasing." Of course "purchasing" something feels like you ought to own it, but did you "purchase" X or did you just pay for limited access to it? That's the entire debate, but this quote baits you into thinking of everything in terms of purchasing / panders to people that already do.

2) This quote amounts to "if paying cannot get you full ownership of X then getting a full copy of X for free is not stealing (so go ahead)." How about you always pay the creator and then pirate only for the additional ownership rights? I'm sure the quote reads that way to some people, but clearly it was crafted to also appeal to the "I just want stuff for free" crowd.