The correct concept here, and I believe this is the way the Bible portrays it, is one of a cancer. You are successful in treating a cancer if you remove it before it actually starts to harm your body. If you discover a tumor while it is doing no harm to you you have the best chance of discovery. If you wait until it actually does harm your chances of success are very small.
Sin is a cancer, and individual sins corrupt an entire society. If you wait until the society is corrupt, it is too late. Just look at the "greed" of the 1980s and they way it actually hurt thousands, if not hundreds of thousands, when the dot-com bubble burst. Individual sins practiced privately - huge social cost.
The tightrope we walk is understanding which of these we can impact by public policy and law, and which we can't.
Homosexual activity is not any near the tightrope. It is way off to the left. That's why it has been illegal in nearly every society in the history of mankind. It is dangerous to let people continue in that sin, even privately. It eventually becomes public and harms a society. Why? That's philosophizing, but if you ask me, it's because those who hate themselves must look outside themselves for acceptance. At least that's probably the way the Act-Up movement started.
On a related note, I have discovered that there are many Yahoo clubs devoted to encouraging people to get fat. I mean chearleeding for people who gain over 300 pounds. Can you see any reason for that? I can only see the reason I noted in the previous paragraph.
Shalom.