'I've never met a human being who has ever expressed a desire to kill anybody'

I have, while Prison Visiting. I actually met two over the years. Both reasonably young and both entirely without scruple regarding killing in certain circumstances. I'm not qualified to diagnose psychopathy, but these two may have had mindsets along those lines. I had no doubt at all that they meant it; one had proved it.

I find pacifism difficult to embrace completely. If my life, my loved ones, my home or my country were to be attacked/threatened I would feel entitled to protect them by a counter-attack.
I tend to agree that human beings have an instinct to violence. But surely we could learn to subdue and control that within ourselves? (Probably not - I don't hold out much hope actually!)
I think it's age, but it's got so that I avoid anything horrendous on the News now. I seem to get very upset, and as there's nothing I can do, I turn it off, stick my old head in the sand and get on with my knitting.