Our culture is rife with such, arenas where (mostly young) people put their life and health at risk for the merriment of the couch potatoes that make up the bulk of the public. We can't outlaw it as long as there are people who rely on it for their livelihood, and large swathes of the populace are insensitive to the sufferings of strangers to the point of enjoying it, immensely.
This is not true. People would do it anyway, it's just that the couch potatoes now provide a way for the people doing it to actually get paid. You cannot be an athlete with your only motivation being 'it'll amuse others'. You need some sort of intrinsic motivation to get at least somewhat good at something. People would fight for fun before the UFC, long before they got paid for it. Same with any other 'extreme' sport. One can argue that the couch potatoes now enable these people to do their activities a lot more, or in more intense ways, but that's a different argument all together imo.