Just going back to your previous point skunk -
If your body is "knackered", then I'm figuring there's going to be no argument as to it's rights - considering your consciousness resides in your head (and I can't see it being cloned, as to transplant the knowledge from one brain to another is nigh on impossible), your rights should theoretically end there.
An example is if you are involved in an accident, where a limb may be damaged in such a way that amputation is an option. I doubt whether doctors will have an in-depth theological debate as to the rights of a mangled limb. And, I'd imagine, you would have no hesitation - if given the option, and the technology - to agree to a replacement limb to be cultured in a laboratory, to be reattached at the earliest convenience.
I saw an interesting (if not, macabre) documentary on Channel 4 about a year ago - it was on people who hated their limbs so much, they would go as far as to have them amputated. And I'm talking about
actual working arms and legs, with no abnormalities. So, after a series of psychiatric evaluations, they were allowed to become amputees. Although I don't believe these people should have had their wish (I think they should be on medication, personally), their point was noted seriously by health and psychiatrists alike - and they all came to the same conclusion to allow the procedures to take place.
If that is the case, then your argument about the rights of limbs is superfluous - there are none.
