That's true but I was looking at it from a resource point of view. Regardless of what we think, there is a finite amount of resources. Should we spend them on an 87 y/o catatonic man or a 6 y/o child? Should we spend them on either if the prognosis is death within a year? It's rough to put that into words but it's a fact.
Think of it in the animal kingdom. The herd of water buffalo may defend the old cow from a pack of lions. But, if the lions are relentless, the water buffalo eventually cut their loss and save the resources they were using to fight another day. They realize that they're just delaying the inevitable. I think most of us would spend our last dime to give our loved one another day. But, once that dime is spent, we're relying on others to provide the resources that we no longer have. The whole "burden on society" thing.
We like to think that the humane thing to do is to keep people alive. Maybe it isn't. For them and for the rest of society.