It should always be up to the ill person as to whether they decide to die or not. If they cannot make that decision, well thats a tough call...but for the times when somebody says "yes I want to die, this sucks, please kill me", I think its grossly inhumane to say "sorry, you have to live like this until you die". Thats a load of bullsh*t and I have a great deal of sympathy for people who aid in the suicide of a fatally ill loved one and end up in jail.
I know that if it is legal it should be strictly controlled, ie. a couple of doctors have to give recommendations, everything is video-taped, etc. etc.