True, but as pointed out earlier, you are better off simply taking 6 purify if you are worried about poison. With sea sponge you have to pay 4
to play it, then 1
to clear only 3 poison.
Or you could pay 1 to clear all poison AND get healing....
As Malduk suggested this card is more intended as a replacement to purify which completely ruins poison decks but is otherwise useless. This card doesn't completely ruin poison decks, but certainly could reduce poison's effectiveness. On the other hand, it isn't completely useless. You could build a rage potion deck with sea sponges and toss in some steam machines. You could also use them for gravity pull if you wanted. They could be mutated if it turns out your opponent has no poison or they could be immolated too.
Anyhow the point is that the card is not totally useless if there is no poison. Also it isn't completely OP against a poison deck.