As I've said in other contexts, the mere fact that giving away intellectual property might, in some cases, make economic sense for the property owner, it's irrelevant to whether or not intellectual property protections should exist. Without such protections, the property owner loses the ability to decide such things for himself.
It's like saying that if someone hijacked a truckload of Toyotas on the way to a dealership and drove them around town, then Toyota should be happy with the free publicity.*
Of course, here's where someone will argue that Toyotas aren't like songs, because if you take away a Toyota the owner actually loses something, where with a piece of intellectual property the owner hasn't lost anything at all. The fact that, when someone downloads a pirated copy of a song, he doesn't have to pay the creator of the song, means nothing, I'm told--which usually returns to the circular argument that the creator will end up making more money anyways, so it's okay. The concept of controlling one's property and who benefits from it escapes some people, I suppose.