One problem is that it already IS public, and will become more and more so. Your statement is like someone saying "I don't want anyone to steal the horses from my barn". Well, the horses are gone, the barn is burned down, and the fence is ripped out of the ground.
It's on the streets, in the schools, forced on employees and business owners, in every form of entertainment and media, and so on. The courts are validating it as we speak, and will continue to try to do so. You are being forced into it with or without your consent. And this is the intent of the gay activists - to change the very atmosphere we live in.
I agree with your point that everyone needs to work on his/her own spiritual life or moral life - but this doesn't negate our responsibility to protect the public virtue, which is right now being viciously attacked on many fronts.
From G-d's perspective, all sin is sin, and lying to our wife about working late when we were out playing golf is just as sinful as homosexuality from that standpoint. But not all sins are as socially destructive. That's why we can justify lying (a sin) to the Nazis about hiding Jews in the attic to impede the holocause (a sin).
From G-d's perspective, both might be equally sinful, but there is a difference.
But your analysis above is spot-on. If more Christians would remember that Jesus came to save us as much as them the world would be in a lot better shape. Unfortunately, most American Christianity is really paganism with a thin veneer of Biblical Christianity glued to the outside.
Shalom.