Is your uncle mentally ill or just very troubled if he has very violent and wicked thoughts and says that he wants to kill everyone he sees but he doesn't actually do it?
Probably both. If this is a real-life scenario, get him checked out. This is certainly not normal behavior and if some people feel this way they generally keep their feelings to themselves. If your uncle was in active duty during the Vietnam War to the present war he could be suffering from depression and should seek help.