It's very troublesome, heartbreaking and expensive to look after those suffering from dementia.
They are no longer productive members of society so can't we just get rid of them in a humane manner?
When my dog was incontinent and could no longer walk and was having seizures every couple weeks my vet told me that it would be extremely cruel to allow him to suffer indefinitely. I took his advice to heart and put him to sleep even though I loved him to death and it was a very painful decision to make.
We do it because we love our pets so why can't we do it for the old folk?