This is always done for only one real reason, and on an emotional level is something that most people learned to leave aside once they had left the 6th grade. Name calling is not an argument!
In fact it is evidence that there is no argument possible to the criticism it seeks to turn away, whether the criticism is overt or implied. One who resorts to name calling essential concedes that they have no counter-argument to the criticism. So instead of actually dealing with the issue of whether the criticism is apt or accurate, they try to attack the character of the speaker or writer, as if a weak character (which everyone has) has any relationship to the truth of the criticism. It doesn't take a lot of brain cells to recognize school yard name calling for what it is, and the people that use it need to mature, and actually begin to address criticism on the ground it is actually made. Name calling is the prelude to school yard pushing and shoving, and that then is the last step before a fight. The pugnacious character of the name caller is revealed then right in the beginning. They'd rather pick a fight than have rational discourse and peace, which in the case of Israel creates dangers to the whole world.
This is not to say Israel is the only place which harbors such juvenile behaviors, for Bush and Chaney show the same immaturity. This would be alright if this posturing would just end up in a fight between those who push and shove, but here we get into something far more dangerous, because such personalities have come to hold a lot of power in a world which far more needs peacemakers than it does children who want to play at war.
