Have you ever been around someone dying from cancer or a similar disease during their last few days of life? I've seen family members go like that, and it's horrible. Why should the patient have to endure such a terrible end when they can go comfortably and at their own volition? We treat farm animals and household pets better than we treat dying people.
And, just to touch on the issue of states' rights, if Oregon voters want assisted suicide to be legal in their state, why should the federal government (or other states) have any right to deny Oregonians their wishes?
A slow human death can be a very long and painful experience. I've always said that I wanted to die under anesthesia on an operating room table. Where your unconscious and feel nothing.
The same way they put people down for the death penalty basically.