I don't know enough about Kissinger to have a strong opinion about him, but I think the idea is that Kissinger got away with a lot of awful stuff because he was responsible for a lot of horrendous things done to other peoples. If Hitler had left the Jews in Germany and Austria alone and just killed the Jews in Poland would that have made things any better?

Again, I am not taking a stance since I haven't done enough research, just explaining why theoretically someone could think that Kissinger committed crimes against humanity without killing any Americans or even violating American laws.