Keep in mind, though, that Pope Francis said he woulkd not judge a person for his sexual orientation. Orientation is a pattern of sexual attraction: it is not the same as conduct.
A sin must comprise "my thoughts and my words, what I have done and what I have failed to do." "Thoughts" in this case means "voluntary thoughts": thoguhts which we entertain or even pursue, such as lustful fantasies and the like.
Thoughts which are outside of voluntary control (e.g. dreams, spontaneous transient notions, etc.) are not sins. They can be temptations, in which case they should be resisted.
Scripture says Our Lord was tempted in every way that we are, but without sin.
True, that some people struggle with that particular attraction as sin, however, according to Romans 1, it does indicate a depravity of human nature that goes beyond the ordinary.
The problem is, if it were only an orientation, or rather a temptation, then there would be no need for anyone to know about it.
Unfortunately, what with the prevalence of gay priests, obviously it is not remaining something unknown.
Another problem I see with it, is that by acknowledging it and not doing anything about it, it tends to foster an acceptance of it, which will eventually erode the stigma, or sense of sinfulness, about it.
I completely agree with your view on temptation not being sin. It only becomes sin when we entertain and then engage in it, even if only on a mental level. Sin begins in the heart often long before it manifests in the actions.