Mainstream Christianity has proved to be extremely vulnerable to the sexual revolution over the past century or so - indeed, the sexual revolution has all-but eliminated Christianity from public discourse in The West, reduced the main Christianity churches to servile impotence - and the destruction continues.
Why should this be? My guess is that many people cannot perceive see any solid link between the topic of sex and the necessities of Christian faith - and the mainstream churches have been unable to explain any link in a way that was comprehensible and convincing.
Traditional Christianity in The West was mostly organized around an attitude that was anti-sex - or was felt to be anti-sex by those who lived under it. The highest Christians were celibate monks and priests in Catholic countries; but everywhere sex was not so much a matter of there being lots of things forbidden (although they were) as that only a very few sexual expressions were permitted.
These rules were presented as divine laws: and not so much explained, as simply enforced.
The problem, I think, is that while people mostly obeyed these laws; they could not understand the link between sexual activities and the Universe as described by Christianity.
There just did not seem to be any comprehensible connection between the Big Picture of God's creation of the Universe and his plans for the salvation of Men on the one hand - and the minutiae of what individual humans did in their tiny minds and feeble bodies: and their sex organs specifically.
The feeling was: why on earth should God care about what I do 'in the privacy of my bedroom'? - or indeed anywhere else? The feeling: what possible difference could my 'doings' make to the Universe as a whole?
Once there was a possibility of sex without babies; sex seemed such a small and temporary thing that it was difficult to see any significant role for it within the scope of the Universe; and mainstream Christianity was only able to provide very indirect, unconvincing and indeed mostly incomprehensible explanations to link sex and God's universe.
This was because Christianity has generally been felt as a spiritual, not a bodily thing; and God Himself was a spiritual and disembodied creator. Men and women were created from nothing, sex was presumed to be absent for the eternity after death - and in general sex was just a temporary and non-vital expedient during the short period of (fallen, sin-full) life on earth
It is a strength of Mormon theology that the significance, the vital importance, the Goodness of sex in the universe is clear in terms of the underlying metaphysics; which is itself clearly expressible as a simple story: that men and women are literal children of an incarnate Heavenly Father and Mother; and our main task on earth is to marry, have children and lead Christian lives primarily organized around families; eternal life after death is organized according to families; and the highest human destiny includes (eventually...) for a man and woman in celestial marriage to become divine parents.
This means that the very fundamentals of Mormon Christianity have built-in sexual relationships, sexual difference and relationships go up to the highest level.
And the vital importance of sex to the Christian Universe is clear even to a child - and without the necessity for long, abstract and philosophical explanation.