The trouble with an attack like that -- albeit a fixable one -- is that if you build a deck that can play multiples every turn, you completely shut out your opponents. So lets say you play it twice, and your opponent puts back two Provinces and gains two Estates to put on top too. That means that player's next turn will consist of at least 80% dead cards. So he probably can't do anything with that turn. Then you play two or even three more on your next turn, and you wipe out your opponent's NEXT turn as well. Meanwhile, you're choking him with Estates, which only increases the chance that there will be extra green cards to have to put back. With Throne Room or King's Court on the board, the problem is exponentially worse.
Bureaucrat is very cleverly balanced, avoiding this particular possibility for total shutdown with its "Gain a silver" clause. If the attacker has to add Silvers to his deck, that means it'll become harder and harder to be able to play multiple Bureaucrats per turn and continually wipe out your opponents' turns.
Sea Hag sidesteps this danger in a different way. This is a card that causes opponents to gain a Curse card to the top of their decks, where it will sting the next turn. To avoid multiple plays of Sea Hags stacking 5 Curses on top of the deck, thereby wiping out a full turn, it has a clause saying that the victim should discard the top card of his deck. Thus, if two Sea Hags get played in a row, the second takes the first's Curse off the top and throws it in the discard pile.
Anyway, it's an interesting thought, having a spamming attack that dishes out Estates instead of Curses. It could be really interesting, in that the junking hurts a deck, but an imbalance of too many Estates might be a difficult point deficit to overcome. It just has to be done in a way that wouldn't be liable to shut an opponent down for multiple turns in a row.
