My brother asked not to be tube fed or given Iv fluid as he wanted to die, he had progressive MS and had suffered 15 years of slowly losing the ability to control any of his bodies funtions.
He was seen by a doctor who agreed that he was in full control of his mind and had made the decision to end his life, the young doctor in A&E who saw him when he was admitted felt that he could not accept the decision made by my brother and inserted a feeding tube and IV fluids.
Once this had been done the doctors would not remove the tubes and it took Mark several more weeks before he finally passed.
I would not wish the suffering he endured on anyone and would have given him an injection at that time had it been a possiblity as we knew it was his wish.
Due to actions taken by that doctor my other brother who also had a terminal condition withdrew fluids whilst he still had full control of his body and hastened his own passing rather than face the same as Mark.
However my Dad passed last year also and he was in great pain towards the end but he was not ready to go and we fought the doctors all the way to get him treatment, to have ended Dad's suffering early would have been against his wishes but would have made it less painful and traumatic for us (he bled to death from a ruptured aneurysm, also had lung cancer). Had his ending been speeded up it would have haunted us forever, as hard as his death was it was natural and that was how he wanted it to be.
I guess the point i'm trying to make is that each case is different and a decision can only be made by the individual, i'm not sure this could ever be policed effectively to prevent some relatives 'getting rid' of elderly relations.
Life is incredibly precious and as much as we can try to empathise, if we are not the person suffering we cannot truly know their wishes unless they are able to express them at the time of the decision