It has to do with "now" because any argument for moral superiority to me would have to come with the stipulation "invalid in 100 years" whereas mine doesn't. The fact that your moral superiority can only possibly last for 100 years invalidates the very moral superiority you're trying to claim today. Such is the case because the future performance of any moral system is taken into account into present performance of said moral system. If you think it's possible to be morally superior today even though such moral superiority is expiry, then please explain.

I know because science allows us to predict the future to some extent. You're right that I can't say "your claim to moral superiority will become necessarily invalid in 100 years with 100% certainty" but I can say "I have evidence that suggests your claim to moral superiority will become necessarily invalid in 100 years with 90% certainty." All I have to do is show you the consequences of your moral system onto a real world population. One example is the ancient Greeks. Obviously any claim to moral superiority by ancient Greeks is invalid because their moral system resulted in their own, and their moral system's, demise.

I take it you do understand the fundamental though, that X has to be, before X can be moral, yes?