Since no one else seems to be answering this question...
Other humans' values have much in common with our own, and if the world were completely destroyed, no life could arise from it again. (Also, not everyone around here is worried about paperclips. Aside from worry, there is also the question of which one you can affect more.) I am not sure what you mean by "worse-than-existential threat", and would be interested in hearing more about this, and why you believe religion is significantly heritable.
You might find this interesting: The Flynn effect.
Religion might not be, but religious thinking is, and given the general continuity of culture over time that amounts to religion being heritable in most cases. By worse than existential threat I mean Christians burning a simulated copy of you in hell for potentially k-large time; it is objectively worse than dying. Dying is just the cessation of future utility, while this would be extremely large negative utility indefinitely.
How does Rationalism as a program square itself with the empirical reality that religious cognition is significantly inheritable, that religious people are out-breeding rationalists, that every large-scale improvement in technology increases the accessibility of that technology, and that many religious people think rationalists should be tortured indefinitely in fire? Given the possibility of worse-than-existential threat from human-value disalignment, why are you comparatively more worried about paperclips?