I agree - any kind of over-focusing on one single skill may make your kid a brilliant baseball player/pianist/chess player/computer genius/whatever, but real life is varied and complicated and we need to equip our kids to be able to deal with that. It's not necessarily that easy, because kids can be incredibly singleminded and competitive without any input from pushy parents too. But they don't have the perspective that an adult has, to see that they're overdoing it, and they certainly don't have the medical knowledge to know that a growing body should only be pushed so far.

Apart from that - I personally feel that many sports are plain unhealthy at a high level, for anyone. The "cutting edge" is just a bit too sharp...

Moderation! in all things.