One of the Mr Meeseeks summons a Mr Meeseeks with the Meeseeks box and instructs this Mr Meeseeks to kill one of the other Mr Meeseeks. But the Mr Meeseekses don't exactly die, they have to fulfill their purpose so that they can go away. So the Mr Meeseeks getting killed by the other Mr Meeseeks would be having its purpose interrupted, which would violate the Laws of the Mr Meeseekses. Also, when the new Mr Meeseeks does kill the other Mr Meeseeks, the new Mr Meeseeks doesn't go away, even though it has fulfilled its purpose. Instead, the new Mr Meeseeks gets swept into Jerry's "Take two swings off my Golf Game" fiasco.