Although I agree with you, unfortunately there are TOO many cats which possibly could be tamed, and not enough people who are willing to do it. That is the problem. I absolutely LOVE socializing feral kittens. My third cat was a feral kitten born to a feral mother on a boat in a Marina. Hence, her name Marina Mar (Mar is spanish for ocean). She was one of the lucky ones, although she is paying for it now because of a immuno-deficiency problem.
Humans are definitely to blame. PERIOD. If they had taken responsibility of a commitment they made when these cats were babies, and had them spayed/neutered and gave them a home, this probably never would have happened. I'm tired of people saying they can't afford it (if that's the case they have no business caring for a pet).
I'm helping my editor trap and spay a female that hangs out on her deck while she reads the paper. She will put her back out when she's ready and maintain her.
Euthanasia??? That's a difficult one. You can only do so much. Especially if these cats have been out in the "wild" for some time. As long as they are healthy and happy and also disease free, I say, keep on doing what you're doing. Caring for them. It only takes a few seconds of your time.
The diseased feral ones, fatal with no cure, as well as the sick ones, also with no cure, well, I'd have to say that it would be in BOTH interests to euthanize them. Why make them go through a horrendous death and possibly pass it on to other pets who aren't vaccinated. That wouldn't be fair to any of them since they WERE here first and didn't ask for this kind of life