Isn't that the crux of the situation with Terri Schiavo? Once she was unable to make her own decisions and her husband and her parents disagreed as to what she wanted, the courts stepped in.
I really don't want to get into this case because the passion is rather high, to say the least. BUT, didn't the court find that Terri communicated her wishes to her husband and 2 other people? (Sorry I'm not up to debating the issue, or if the individuals had a motive or bias.)
I rather talk about my own situation, and the legitimate (or illegitimate) right of courts and the legislature in MY right to death with dignity.