The only reason one should not lay judgment on another person is because it is believed that by doing so we will bring harsh judgment on ourselves. While this is true, we also must realize that our sins {however bad they may be} do not come near the sins of a terrorist who has killed Jews with intention to kill all Jews. There is a balance of judgment, as I explain to some of my friends from time to time. We must be able to judge the evil which is very evident in the world. We should not judge people who have sins which are on the level of our own sins, because if we do so, we are inviting divine judgment on ourselves.
This is what I understand...