Why do Europeans think killing Osama was wrong?

I do not understand why anyone thinks killing that man was wrong. He was a disgusting man who stated himself he sees all Americans the same, civilians and the military, he had no conscience and he would have attacked us again. He is barbaric and personally I believe he should not have even gotten a "burial", his group hung the people they killed as trophies, we should have done the same. Oh no but that would not be okay. UGH I am MAD