Is it a uniquely Anglosphere phenomenon (by virtue of American cultural imperialism, of course) that there is a serious debate between "conservative Christians" and "LGBT et al" over whether or not homosexuality is a choice?

And just like every debate that manages to filter into the conversation of common people, both sides opt for the extreme: for conservatives, it is a conscious choice to not be heterosexual; and for progressives, a person is simply born gay. Both wrong, both stupid.

Then how does gayness come about if both are wrong?

Though humanity particulates into two sexes, sexual communion between them brings unifying reversion. This temporal reversion conjoins them into an immanent 'one', a state participating of god - a oneness and union mirroring the oneness and union of the divine itself.

But as with all encosmic things, our primal knowledge of sex is that known via sense. This level is little different to that of other species; desire is for the act alone, not for the union or product. For those overwhelmed by indulgence, having a sex preference is preventative.

This kind accounts only for a small number, however. The majority of those who peel from the sexual norm have so due to certain sensible 'impositions' impressed upon the mind from without, their material conditions inducing a reaction that results in novel sexuality.

Although explicit study into causes of sexuality has become a minefield due to politics, it is known that the frequency of having been a victim of historic or ongoing abuse (sexual or domestic) among those who identify by novel sexualities is disproportionately high.

Culture has also increasingly normalised novel sexuality, pressing it strongly among youth through sex education and media. Alongside this is consumerism's encouragement of selfishness and its glorification of frivolous and indulgent lifestyles.

This is just absolute speculation.

It's not speculation, it's Platonic metaphysics.