Guilt is not always a bad thing. It helps prevent us from making the same mistake over and over, also driving us to do certain acts to appease our guilt. What would make you feel better coming a person who felt guilt. An apology or action to attempt, at least within their head, to right their shortcomings/mistakes? He has not commented one way or another, or expanded any. I am simply offering an angle being ignored, not that one way is more right than another. There is not enough information to decide right answers from wrong answers, but I do not believe we can ignore the full picture until what we should be looking at is revealed.
Let's not take a wide brush to guilt as a bad emotion.
I will not begin to even try and say what he experienced. Fact is though, people react differently. You can thank evolution for that one. I would not be surprised being subjected to war could result in a return with a greater value placed on life, in some people.
Vegan? Having a respect for life does not mean unwilling to end an life. It means you do not take it lightly, and only will, if absolutely necessarily, such as hunger or self-defense.
Why? Because no one person can ever save EVERYBODY. What you can do though, is do what you can do. Essentially with that argument you are telling me there is no point to getting into medicine as I will be unable to save everyone. Norman Borlaug is credited with 1 billion lives saved. I live in reality though. We may only ever get 1 Norman Borlaug a century. A person who has proven their worth to the world past, present and future for 100s to 1000s of years. But we have 7 billion people on the planet, and if 1 billion save 1 creature's life in their life, everyone be a part of being the next Norman Borlaug.
Guilt of a single mouse can be a good thing, or a bad thing. Do no rush to paint it as an absolute bad. The guilt of this mouse can be used to drive a person to care about the next mouse. When you are getting into a business you simply can not win, you can not run on logic. You can not cheat Death, and Death always wins in the end. But you can not let it know you know that. When your business is respect for life, logic leads down a dark and very deep hole. It leaves you asking yourself, "What is the point?" because it IS pointless, everything dies, there is nothing you can do to stop it, why am I even trying, your 3 year old son is going to die anyway one day, why not let it be right now? Why remove the tumor that can extend his life to normal expectations?
So you are right, billions die a day and that is why I would care about that one mouse. It was the one out of the billions I could possibly help and maybe, I don't want to die just watching it happen. If I am to die, as I will and am one day, I will do so with my pride and conscious free. If on my deathbed, I felt I did all I could, I can wash all that guilt away and die guilt free. Until then, I need that guilt to make me do everything I feel I can.
So, the argument is not about guilt, veganism, feelings, or 'preserving life'. It is a perceptual issue, as everything you said is only as bad or good as the perception through which it is used.