What role should the future play in decision-making?

Expected values are important. Obviously. Couldn't you have asked that, instead of bandying about with discount rates and chess?

It is not clear to me that prohibiting murder derives from that position or mandates birth.

I don't think prohibiting murder is the thing to do because having more people in the world is a net positive. I think it's the thing to do because prohibiting murder is a net positive, for reasons I've gone in to elsewhere and will happily repeat for you if you'd like. But I don't see that prohibiting infanticide has the same positives. If the reason you're against infanticide is that you think increasing the number of people in the world is gives a positive expected value, that's fine - but then shouldn't you be having as many children as possible? If not, I'm having trouble seeing what relevance it is that a fetus is going to be a person.

I believe this addresses the rest of your post, also.