I think there's some truth in what you are saying.
Euthanasia has been around for as long as humans have been around and it was often the local wise woman, nurse or witch who would be there for a person in great pain. And it was them who would help that person let go of life as a kindness. There's nothing sinister about this - it's a very human thing to do.
This sort of thing was never talked about, because we've been told that it is wrong. But someone needed to do it and this act of kindness often put them outside of the community and caused them persecution.
I Shall Wear Midnight, in particular deals with this 'unsaid contract' between the public and the witches. No one wants to acknowledge what goes on, but people are often glad that such people exist.
Terry seems to, quite rightly, want to make people talk about this. People wouldn't even mention (for example) the word 'cancer' a few years ago. Now it is talked about, discussed and better understood. Talking is good!
“Men never commit evil so fully and joyfully as when they do it for religious convictions.” – Blaise Pascal