My heartfelt opinion is that as knotty and challenging as assisted dying is in practice, the sooner we get the societal and legal framework in place for it, the better.
A PP mentioned the Hippocratic Oath, but of course Hippocrates had none of the arsenal of modern medical tools with which life can be extended. I'd argue that "first do no harm" is hard to reconcile with endlessly prolonging the existence of someone who is suffering and wishing for a speedy, rather than drawn out, death.
I'm mindful of what you hear on the pet boards all the time regarding loved animals being PTS: "better a day too soon that a moment too late".
I understand that it's much more emotionally and morally loaded for humans, of course. But when all is said and done, my late dog had a far better, kinder death than my mum did. And that MUST be wrong.
We need Dignitas over here, ASAP.