Leaving the moral issue of killing yourself aside for a moment, just take a look at the practical issues. Consider:
You're a nonbeliever with a terminal illness who abhors the thought of dying by inches dribbling and vomiting, etc. So you go along with the "compassionate dying" crowd who insist that killing yourself is easy and pleasant, no problemo -- except that the drugs leave you "gasp(ing) and snort(ing)", vomiting and having seizures for hours before you finally experience that blissful nirvana of the good death. Nice picture, eh?