It's a good question, and takes more than a line or two to answer.
I'm a life-long hunter. Over the years, hunting has put much meat on my table and in my freezer. But I have gone "deerless" for the past two years, and not for the lack of opportunity. This past season, for example, stretching from mid-November thru the end of January, saw me with chance after chance for fine critters. Each time the outcome was, more or less, "Nah, not this time."
The attached image shows one of my many cervidaen visitors. It's an infrared "trail camera" picture of a buck that practically lived on the place all winter— finally depositing one of his antlers in the front yard by the porch, perhaps a gift. (In the picture he is standing a measured thirty feet from the house.) He was in my sights several times and the decision guiding the trigger finger was always a "No." Why?
I'm not sure I can answer that question very intelligently. Perhaps still having venison in the freezer has something to do with it? Maybe. But that's not the whole answer, or even most of it. I think I have just reached a point in my life when I have no desire to kill much of anything. Killing was never the best part of hunting for me. In success there was always a measure of regret along with the satisfaction of having "made meat" as the old-timers used to say.
Nowadays, immersed as I am in the day-to-day flux of nature and her many critters, I feel I have nothing to prove to myself or anyone else with regard to my ability to take animals for food. (Trophies have never interested me at all.) Younger, more eager (and perhaps "macho") hunters would surely call me a wuss. That's OK. I really don't care and I don't need their approval.
Bird-hunting is slightly different. It's not at all a solitary activity. I am in the field with at least one of my dogs, usually both, and often with several other hunters and their dogs. It is almost a communal pursuit. Following behind and watching the dogs work is one of my greatest pleasures. I could easily do it without a gun, but the dogs will have none of that. The point, the rise, the shot, the retrieve— all are at the very center of their lives and it is no rationalization on my part to say that to deprive them of that whole process would be a cruelty I cannot bring myself to be a part of.
If I choose not to take a deer for my table it should not be taken as a criticism of or a rejection of the practice and ethics of hunting. It definitely is not. I believe in the value of hunting both as a means of responsible conservation and a personal pursuit for sustenance, both physical and spiritual. I'm sure I will take deer again, perhaps when the freezer is empty, or when I feel that the time is right. When that happens, the little voice will say "Yes!" and I will act accordingly.