I offer you the evidence of history, and Card's OWN ARGUMENT, that fantasy ideology can and does overcome "basic desires" for entire swaths of the population and entire generations.
It is empirically unassailable that MANY religious people actually value the next life more than this one, and make life-changing and life-ending decisions based on that belief. I'm not asking you to agree with said belief; I'm asking you to apply Occam's Razor to an observed phenomenon.
Simplest explanation: they believe it. For them, they no longer desire grandchildren; they desire the best end for their children, which, in their view, is martyrdom. Their parental love is intact; their story re-directs that love to an erroneous end.
You make a compelling argument, but my question remains: What do you propose we do about it?