What are the advantages of euthanasia?

I think the reason people have such a huge problem with euthanasia is because of the genocide it could lead to. Hitler originally titled his eradication of the Jews euthanasia, but we know how that turned out. I believe that morphine is a type of euthanasia and I think that is a good use of mercy killing, personally. But again, euthanasia and genocide have been characteristically tied hand in hand.