I think it depends.

If you're 19, and you decide that you have nothing left to live for, with no acceptable medical condition, I'm not prepared to say that it's a reasonable decision. You haven't decided that there's nothing left to live for, you've simply chosen that it isn't worth bothering. I think that goes against any ethical stance that a sensible physician could take.

If you're 80, and your physician has told you on no uncertain terms that you will decline, either mentally or physically, and die, a dignified process is not only acceptable, but important in recognizing individual wishes.

However, this opens up a middle ground, and I think it's helpful to consider this from a physician's standpoint, if you were given the final decision:

Middle aged woman with a chronic pain condition who wants assisted suicide. Has relatively good quality of life by outside observation -- able to move, walk, conduct daily duties, but constantly complains of severe pain.

Younger man, let's say 27. Medical history of cancer, with detailed treatment history, and an involved, highly emotional family, by his side throughout every process. The treatment fails, further treatment options are available, however, he requests assisted suicide. History shows good progress with treatment, but no full remission.

Older man, presents to ER with myocardial infarction (heart attack, in the most serious way) receives treatment. Outlook is good, however, uninsured (US. This happens.) patient requests assisted suicide, refuses to clarify reasons.

TL;DR: All of this is bullshit, and you should read it as such. However, my point isn't to discredit assisted suicide -- something I strongly believe in -- but we have to do it right, and there are a lot of outside factors in play that make it a difficult thing to do properly.