There is no way to ban hacker's address. He can move them around thru different bitcoin services, then sell them OTC or use them to buy something, then what? Someday you will get some of the coins that came from his address and mtgox will blame you. This is stupid, but completely expected from mtgox.
no it's not stupid, it's ethical and it is the bitcoin community regulating itself ( buying/selling drugs? cool Stealing bitcoins? not cool)
those bitcoin services will have to check if these bitcoins are suspicious before accepting them, otherwise they might have worthless bitcoins in their hands