Assisted suicide is merely a suicide assisted. Just like for me to pull your wallet out of your pocket would be a criminal offense, but it would cease being an offense [and I could not be called a pickpocket] if I were to do it at your request [say, you have an injured hand or something]. Ditto here. Assisted suicide is no different in the degree of criminality than an unassisted variety.
The justification, most frequently cited for *assisted suicide* is for there be a physician present to ensure "nothing goes wrong." If the party who had previously consented to suicide, hesitates or waivers at the last minute, but is incapable of communicating that thought, the physician would almost surely interpret this as his cue to step in and consummate the act to ensure nothing went wrong. It is giving the physician (or simply the assisting party) the ultimate authority over the decision as to whether or not the person lives or dies, and does not honor the final wish of the patient. That is euthanasia regardless of any term you should use in its stead.