Is that an argument against voluntary euthanasia though?
My parents have both told me they would sooner die than go to a nursing home. Knowing them, I believe both that they mean it and that they would be utterly miserable in a nursing home. Obviously I would be distraught if it came to that, but how selfish would I have to be to tell them "no, you must go to this place that you'll hate because of the impact it will have on me if you die"?
I certainly think there should be controls. A waiting period, mandatory psych checkup to validate rationality and sound mind. If those (quite low) bars are cleared though, I don't see any reason that people shouldn't be able to choose to die.
To your second point, doctors don't necessarily need to be the vendors of legalised euthanasia.
A rheumatologist friend of mine once expressed that he is generally supportive of the idea of voluntary euthanasia, but believes this should involve creating some kind of "assisted dying professional" role. Asking doctors to euthanize people creates (as he put it) a kind of conflict of interest; the person who is there to help you live should not be the same person who can, if you choose, help you die.