Thr guards job is to protect the King. The only way we can protect the King is by making the assassin unsure who the King is. We have to make the assassin believe there is a possibility we ourselves could be the King. If User can no longer do that he is useless as a guard and he could also possibly be the assassin. Would you rather eliminate someone who has not already been outed?
I have to agree with Tay about even if they are known to not be the king, they can still help.After 4 votes User was a done deal. He was guaranteed not to be the King at that point. If I was the assassin I would have wanted to keep User around and take out someone else so I would know who 2 people were. Now the assassin knows only one of us.
You say if you were the assassin you would want to keep them around...I guess I don't get it, but why exactly would they want to keep a pretty much "known" guard around? The assassin knows ALL of us are guards, how can you say they only know one of us now?