Royston, I question this.
"After a long time the profession came to the realisation that homosexuality could not be treated. It had no symptoms, it was natural in other species, as well as humans"

It can be said to have symptoms. That is how it is recognised.
There are many conditions regarded as diseases that occur in other species as well as humans.
No treatment has yet been found, but it may.

We may not regard it as a disease, but that remains a valid point of view.