If the person who is suffering wants to get it over, why not.
I wonder how many religious people have had their pet put to sleep?
Do you know what. I was amazed when soembody texted sky news to say that it was very selfish for somebody to want to end their life, in such circumstances and felt that the person was being selfish to the rest of the family. Unbeleivable.
If you are not selfish, you would not want to let somebody suffer just becuase you couldn't live without them.