"but why is a rebuilding team allowed to trade a young stud for old ones?"

If a team wants to trade a young stud for an old one you are in favor of not allowing them to ? Having a baseball "god" who oversees and disallows trades that are equal in talent but, in the gods opinion, bad down the road is the quickest way I can think of empty PB of owners with brains. Who is going to make these decisions ? Mike ? He knows an awful lot about baseball but I don't wanting him telling me what I can & cannot do for my team, based not on whether the trade is fair now, but on his crystal balls vision of the future.
I can give you dozens of examples of trades like this that worked for either team, you just can't predict the future.
I'm all for leveling the playing field (PB cap, lowering the keeper roster,etc.) but ranting about trades that are fair but may work out better for one team down the road (and you can't say which team will benefit most!!!) and talking about not allowing owners to make trades they want to is big-brother, socialistic BS.
The smarter owners will have good teams, that can't be helped unless we just flip a freaking coin to decide the champion.