Committing to multiple teams seems unethical. It's one thing if you realize you made a mistake and you need to do what's best for your kid, but intentionally keeping several teams on the line thinking you're with them then jumping ship on them is pretty awful, IMO.
I agree with you completely, but I have seen it done MANY times. Typically organizations will learn who these people are and won't even offer them spots, no matter how good they are. But if they are good enough, someone will take the chance.