..."according to Holy Scripture and thousands of years of Tradition, homosexual behavior is gravely sinful? It is through this very behavior that that homosexuals estrange themselves from the Church.".....

You are right about this being the source cause of anti-gay attitudes.
Question is, have we reached a point in our knowledge where some ideas need to grow and change? Can we ask "Why" these former judgements were made? 

True enough, same-sex attraction is not the 'norm', and the majority of people are attracted sexually to the opposite gender. So most 'feel' funny about it. They don't comprehend it. But does that make it morally 'sinful'?

That's the sort of question people of today are asked to grapple with. Even if only one person in the world is different from everyone else, does that render them abhorrent?

Can 'truth' go beyond "thousands of years of Scripture and Tradition"? the human race is will continue to be propagated, even if not everyone contributes to it.