can you accept the pet euthanasia?

I think it's the only humane thing to do in some cases, my friend had a dog that was 17 years old, the poor thing couldn't see or hear & kept hurting itself, falling down & such, it also had arthritis yet she refused to have it put down coz she couldn't live without him but i felt bad for the dog coz all pets need a quality of life & if there's no quality, then it's just cruel to allow them to continue living. If it's an incurable disease then of course, you have to think of how the animal feels, not just how sad you'll be when he's gone. You cant expect an animal to continue living if he's in pain - that's just selfish.

If that incurable disease causes pain and suffering I would euthanize my pet. I don't want it to go through misery for my wish to keep it alive.