Unlike abortion (not a good analogy) the issue of consent would rule over euthanasia. I agree that it needs to be watched, can never become a situation where it is judged in terms of the expense of keeping people alive and there is always a danger when you bring it in people may be pressured by others. Therefore extreme safeguards would need to be in place and it should never become 'cool'.Because it's humane and merciful. I do take your point - in certain, limited cases, euthanasia is arguably humane/merciful. But again, the obsession with the sanctity of the individual at the expense of the common good is gravely concerning. Sacrificing Sanctity of life in favour of quality of life has serious repercussions for society IMO. So, like abortion, where do you draw a distinction between Sanctity of life and quality of life?
The other two points are valid as well. It's too simplistic to compare humans with animals; it's a crude comparison. We don't foist our own moral dictums on animals so why use such a comparison to advocate in favour of euthanasia for humans?
I used the animal comparison because it is valid, we euthanise pets because we don't want them to suffer unneccessarily and we can't ask them what they think. Not a perfect analogy true but every pet owner who loved a pet felt anguish and extreme discomfort at the decision.