And some Muslims see no problem killing other Muslims because they aren't the right sect of Muslims, and some Jews see no problem with killing Palestinians because they are Palestinian, and some Atheists have no problem with killing Muslims over parking spaces, and some blacks have no problem killing other blacks over the color they are wearing, and so on and so forth.
People suck and a whole lot of people have absolutely no problem killing other people for the slightest of reasons, or any reason at all. Religion is just anther flimsy justification that some us but if truth be told, most of us can be convinced, or convince ourselves, that hurting someone else is the right thing to do. It's just a flaw in human nature.