If you are scammed for an account or paypal, you are welcome to recover the account or funds. (As long as you have proof that he recovered first; otherwise, you are liable to get banned for scamming.) However, you can't go chasing after him trying to scam him, nor can you scam someone else who you know or think is a scammer.
There are enough scammers on this site as is, without encouraging users to get used to doing it themselves. Think about it: if someone breaks into your house and steals something, the solution is not to break into theirs and steal it back.
Counter-scamming opens the door to numerous other problems - ie, to users trying to justify scamming more than was lost, scamming traders who 'would have' scammed them, scamming those who they think might have had another account who scammed them, etc.