[nl]

I think most elite athletes already jeopardize their health from too much physical activity. Consider traumatic brain injuries in the NFL or boxing

NFL and Boxing are sports where brain injuries occur when doing the sport by the rules. I - and many others - think that is unacceptable, and in the NFL at least there seems to be at least a small amount of movement to improvement to this.

or wearing out your knees from running on pavement for hundreds of miles.

There's plenty of evidence showing this isn't really a thing. Humans evolved to run long distances and while modern high level sport is generally at a higher intensity this doesn't seem to cause "wearing out of knees".

OTOH, many "runners" (even healthy ones) are much much heavier than the weights we evolved at, and there does seem to be a link there.