You know how you're not supposed to clap between movements at a classical music concert? (you're supposed to wait until the end of the entire piece.)
Many classical music snobs hate that sort of ignorant clapping. I read an interview with a famous conductor once about this. He said, "Actually I don't mind at all. It shows that we have new people coming to our concerts, and I think that's great."
People cheering at the wrong time at a football game shows us that the games are attracting new fans. I'd be careful before condemning it too harshly.