Your argument is excellent by try getting them to listen to it. They will only say, “But we were born with special digestive systems which can only digest pears and not apples.”
Of course they will, but that has nothing to do with the argument. And it's not them we'll be trying to convince, after all, but ourselves. We need to stop letting the other side define the terms under which we disagree. Like the devil, they use our sense of honesty and fair play as a club to beat us with.