well, it's human nature for a sane person to want to continue to live. That means if one chooses to die, they are of questionable sanity and therefor, incapable of making a such a life or death situation. That can be used as a basis to force feed them. If they are unconscious, again, one would presume they did not wish to die and as such, they get treatment.

In any hunger strike I recall reading about, they did not force food or fluids upon them while there were capable of refusing it. Once they are unconscious, it's fair game.