Ramesh — yes, I was imprecise in my use of the word “massacre.”
However, my point is not that if X happens naturally with great frequency, we should let people do it deliberately. My argument is that if X happens naturally with great frequency and we do not see this as regrettable enough to try within reason to stop it, we’re being inconsistent if we forbid people to do it deliberately. In this case, we’re seeing an embryo as a human being when someone is deliberately destroying it, but as an item of no concern when it is destroyed naturally. In your example, we do in fact go to great lengths to stop the natural deaths of the elderly, so it is not inconsistent to forbid killing them.