I have killed my own food before a number of times.
I have not. But I have killed many animals for science research. Specifically, I harvest brain cells to (hopefully) advance treatments for stroke. I don't talk about the specifics of the work I do around people I don't know well, because you get mixed reactions. Many people think that I'm a monster, but I'd say most think it's a better than even trade for humanity.
My experience over the last eight years since I've been doing this work has been mixed. The strange part is that you really do get more used to the killing. What used to bother me a lot in a physical sense, now doesn't bother me at all. That it, I don't have a negative visceral reaction to killing, but I definitely did when I started. However, the flip side is that I feel less and less comfortable with the idea of animal research the more I do it. I wish there was a better way. Maybe one day there will be, but I tend to doubt it. These systems are complex enough that it's difficult to imagine that a computer program could ever replace a mammal. A bacterium? Sure. But a mammal is a whole 'nuther story. At least for the foreseeable future, I think if we want to march forward with medicine, animals are the only way.
It does raise an interesting calculus about the value of a rodent, dog, or monkey vs. a human. How many dogs are worth saving a congestive heart failure patient? I don't know, and I think the assigned values are basically arbitrary. It's up to each of us to decide for ourselves whether research, or eating meat, or destroying habitat for a home to live in (something pretty much all vegetarians do just like the rest of us) is worth our comfort. I detest factory farming (which I see as a completely different topic than eating meat by itself), but as a moral judgement, I would never try to convince anyone on either side that their position is wrong. Too complicated for my small brain.
(I am also an organ donor. I don't see any good reason as to why anyone wouldn't be. But it's also a topic a wouldn't debate, because people who are against it get surprisingly heated over it.)