If you understand the Talmud it all makes sense. Gentiles have no souls and were created by God to serve them. They are no different from a hammer, or a sewing machine. Simply tools. Would you feel bad about smashing up a broken down sewing machine? No, it is just a machine. That is how jews feel about non-jews.
There's a greentext out there written by a jew about how jews view gentiles like a gamer views NPCs.