The goal behind altruism is to improve the quality of life for the human race. The motivation for altruism maybe due to evolutionary reasons such as propogation of the species etc., but it is not the same as altruism.

This post is however about the latter as you have rightly pointed out. Nevertheless,

When human lives are at stake, we have a duty to maximize, not satisfice

and therefore, the way to go about maximizing is to first ensure that all people currently alive remain alive and well taken care of. After that there's plenty of time to go about having more babies :)