...On the other hand (continuing from where I left off earler), intellect is genetic, and, *ahem* people of a higher intelligence are more likely to question the social strata of their society, religions included. They will seek actual answers to their questions, and with their pursuit of knowledge, overcome their religious disadvantages. Now, there are outliers, and people can be incredibly intelligent and religuous.. but.. *digs up charts*
So, in a sense, religion have a genetic basis (not the religion itself, but the inclination to actually believe in it), but it's still mostly environmental, arguably the antithesis to homosexuality.
If no one has heard of particular religions, they won't come back. If no one has heard of homosexuality, it will still happen because it feels natural to those people whereas religion is, lightly put, brainwash.