What do you mean by ‘natural?’ I use it to mean that something flows from and is consistent with our nature (human nature). We all have a natural desire to continue the existence of the human race. Homosexuality cannot effect reproduction thus those acts are unnatural–that is–homosexual acts require using gifts (sexuality, reproductive system) against what they exist for (reproduction), against their nature.
What is natural is what occurs in nature.
That which happens as a result of something’s state or structure.
Something unsophisticated or contrived.
You clearly use natural in an un-natural way.
You look at creation, try to deduce its purpose, then if you find something which does not comply with that purpose, you consider it un-natural.
It is a great hubris to imagine that we can deduce the purpose of creation.
It is great hubris to imagine that we can understand the intricacies and methods the Creator set in place to drive that purpose.
There are many seemingly illogical intricacies in this creation, which the short-sighted see as evil, but their removal would have a deleterious effect on the creation.
Consider bugs, germs, viruses, poisons. They all seem evil, but they all serve a purpose in balancing the creation.
If the Creator had intended that two sexualities only were to be possible, that would be easy to effect.
The XX, XY pairing could have coded directly for sexuality, but it doesn’t. It only sets a proclivity: makes a probability. A sort of ‘free will’ on a micro scale if you like.
That the Creator set things thus, shows that this must have been the intention.
Who knows, it could be a shiboleth to test us as to how we will react to what is different, and it seems that to date, many of us fail the test.