A legitimate argument against euthanasia is that it would be used as a replacement to further access to healthcare. In any country, you're never really going to see the rich use euthanasia unless they're very very old or at the very very end of palliative care because they have access to quality of life enhancing medications, physical therapy, and technology.

A country without universal access to healthcare, such as the United States, would see an inordinate amount of poor people choose euthanasia due to their inability to access healthcare. A real life "have you tried killing all the poor?"

The UN Human Rights experts have raised this concern with Canada, a government which approved of a 61 year old's medically assisted euthanasia when his only significant impairment was hearing loss...after he was checked in for being a suicide risk. European countries seem to have more stringent laws and better access to healthcare, but the solution to a lack of support for the impoverished can't be government sanctioned suicide. That has to be incredibly limited in scope.