It doesn't make me want to vomit anymore, but it took quite a long time to get used to.

I know the feeling. One of my jobs at a restaurant included emptying the mouse/rat traps. I don't know why the boss wanted to use humane traps, since we were in an area where we couldn't really let them go. Lucky me!

I think what bothers me about how prisoners are executed, is as you pointed out, that people don't want to take responsibility for the action. Thus the traditional executioner's hood. I admit that there are some people who cause such great harm to their fellows and the society they live in, that execution will be a viable solution. I don't think that lifetime imprisonment is a humane practice and I think that at this point, correctional practices and techniques can only be so effective and only for willing participants.

That said, I do think that we all should take responsibility for the killing of prisoners, but diffusion of responsibility is very real. If there were some way to impress the personal responsibility and burden of killing on each individual who benefits from it, as well as support structures in place to help people understand and deal with those feelings and experiences in a constructive way, I think that we might all be better for it. But, that's still firmly in the realm of science fiction, as far as I know.