If you have no chance of living or dying peacefully, then yes you should be quietly allowed to pass away. That is our right and no one should hold judgement over that but the creating forces.
No, it shouldn't be legal, because it's murder regardless of how you look at it, and we could never know for sure that a cure for the illness you suffer from won't be discovered just a few days after you legally committed suicide.
Absolutely it should be legal. I mean if someone knows they're going to die and they have no chance of recovery (like a stage 4 cancer in their brain that can't be removed/treated) and are faced with a slow and painful death as their body shuts down on them... They may want to be able to end their life on their own terms before they have to put their family and friends through the months of agony watching them break down.
If anything, I think denying them the opportunity and forcing them to endure it would be considered cruel and unusual punishment. We protect convicts from going through that, so why would we then turn around and force someone who's sick already to suffer more?