But I don't understand why the Paypal scams are have to be the problem of the trading site? Why don't you tell your users that there is a high risk if they trade bitcoins against Paypal money? Everyone is free to choose what they accept as payment, including the pros and cons.
If you read the thread carefully, you'll notice that Mahkul mentioned that the scams were flooding their support system. Since they're free, they can't just throw money at the problem to make it go away...
It isn't ideal, but until they get the rating system implemented, this is probably the best solution.