Why? Because in places where this has been tried and normalized, people are finding out that the One Judge you are referring to is being superseded by human judges making the decision for them. Once you normalize the idea that some lives "are not worth living", you open the door for others to decide which ones fall into that category, whether they would choose it or not. Where is free will when it is the deformed being euthanized, and then the mentally retarded, and then the decrepit, and then the inconvenient 3 year olds, and then the gypsies, Jews, homosexuals, and whoever else has a life not worth living?
This isn't theory - it is happening in Europe, not for the first time either, and you can see exactly the same thing has happened here, once "It's a woman's body, so it's the woman's choice" became normalized enough for people to discount the other body involved. The death culture advocates are following the template of Roe exactly.
Also because in many instances it isn't a case of suicide, it's a case of death by doctor. "Assisted suicide" is another one of those phrases of art that are trying to be normalized, but are oxymoronic lies. The patient isn't self killing; the doctor is offing them. I, for one, don't feel that those supposedly dedicated to preserving life should be perverted into the licensed takers of life. It soils the professional ethics, and leaves a huge gap for abuse by death-obsessed M.D. psychos like Kevorkian.