I believe safeguards could be built in so the law can't be abused easily -- the assistance MUST be requested by the patient, not family members or anyone else; at least two doctors must agree that the patient is terminally ill, the patient must be competent, etc., etc., and there must be a waiting period. I don't think people should be allowed to just walk in to their doc's office and announce "I want to die" and get the meds to accomplish that. I do think a patient should be able to make the request ahead of time, if he or she wishes, like "if I ever get to the point where I'm _______________, then it's time. Kind of like a more aggressive living will.
I agree strongly with AZ Jim above that a patient should never be forced to endure through to the bitter end, if he or she does not want that. A family member was recently in that situation, and the bitter end of metastatic colon cancer was FAR more inhumane than just letting her go in peace with maybe too much morphine or anesthetic or something.