The price of labor, just as any good or service, is determined by supply and demand. You might think that the salaries, advertising, and ticket prices have gotten out of control. Hell, many people might think that. Enough don't, though, and that's one reason we still see increasing salaries for professional athletes.
On the supply side, I'd argue that it's less probable for someone to become a professional athlete than it is to become a teacher, nurse, or veteran. In the former situation, a person basically has to hit the genetic lottery. The latter situation can be reached through learning and training, which is far more easily attainable for the average Jane or Joe. I mean absolutely no disrespect toward any teachers, nurses, or veterans. It's just a game of numbers -- how many professional athletes are there in the world in comparison with how many teachers? What about nurses or veterans?
I don't think the statement that athletes fail to contribute to society in a meaningful way is correct either. A society without entertainment wouldn't last for long. I think what's more important is the sense of comradery fans of the same teams feel. "Oh, you're a fan too?!" In a way, sports teams help bind communities together. Just look at this website as an example.