Ok, so what do you suggest that people that haven't experienced the exact same thing as you say instead? We are simply human beings and we all have different moments in this thing we call "life". You chose to go and spend those by killing people in a specific place on this planet for some sort of cause you believe in, while I do other things with my life in other places of this planet. We end up having different lives, with different ways of looking at things, because we are ultimately shaped differently.
Say I'm a person who doesn't know how to respond to you telling me you went to war. It might even be something that makes me unsure of how I feel about you. Can you not let me be human like that? Am I really that bad for just reacting? I have to think exactly what you are thinking and reacting in the way you would prefer?
It's very simple. Since I didn't go to war, I don't understand you. I don't understand your experiences, I don't understand why you did it, what it means to me and I don't understand how you feel about me not going. I don't understand it, so like the unknowing primate I am, I just repeat what everyone else is doing, because that must be correct, right? So I say 'Thank you' and let the awkward elephant into the room.