In my opinion many on the left (The DU /MoveOn types in particular) are actually glad when things like this happen, because all they care about is defeating Bush, no matter the cost. Apparently, you disagree. That's fine.
I have to agree with the other poster - I am conservative and have also opposed this war from the beginning. Say what you want about the American left, but I have seen no one from either side of the fence "dance with glee" or whatever when Americans die in Iraq. If they really somehow relished the idea of Americans dying, I think they would have supported - not opposed - the war.