I know this is a slippery slope, but having watched my grandfather for months slowly dieing while we stood by and could do nothing for the pain was horrible also.
I have stood outside abortion clinics and protested, but for a grown adult who wakes up every day wanting it to be their last due to unmanageable pain or a disease eating at their mind I believe that is a completely different topic. We all know that some doctors will help a patient along at the end, letting it be official is something a free society should consider.
Unfortunately, the left wants the power to kill at their discretion while trying to sell it as individual choice.
Look at the ogreish practices in the UK and Canada (denying food and essential treatments). They cannot yet kill outright so they make do with the tools at hand.
If you allow euthanasia you've let them get their foot in the door.