The government needs to uphold morality.
1. It's only immoral by the Bible. Separation of church and state. There is no national religion because we aren't a bunch of witch-burning puritans. Bringing religion into a political discussion is instantaneous failure in my book. Despite any religion I may follow, I think politics from an atheistic point of view because that's how our country was built. With freedom in mind.
2. No they don't. The government doesn't tell me not to lie to my parents. The government doesn't tell me not to swear to my peers. The government doesn't tell me not to flip off bad drivers. I don't do any of those things because I believe they're all crude and I have some amount of self-control.
3. Now, your orientation, like any other like or dislike (and in a more dark zone, fetish), you can't choose or fight. I've tried to force myself to like things before. Coffee. The kinds of music my sister likes (she was the one trying though, but I tried for her). Green beans. When Pokémon went out of style "because we all grew out of it," I tried to stop liking it. Couldn't. Didn't play for a long time but eventually came back. Drug or alcohol addictions can be overcome, but notice the difficulty. And it's not forcing yourself to stop liking it so much as forcing yourself away from it. This is all anecdotal evidence, though. Go ahead and find those sources, Chup.
4. Again you are failing to answer my question (because there is no answer to "how does homosexuality hurt other people" except for "it does not.") Likes and dislikes that hurt people can be outlawed--some people like to shoot people. Some people don't like to tell the truth in court. These result in pain for others. Love lives are very different. You see two guys. Big deal. You see two guys holding hands. OKAY NOW IT'S TIME FOR GOVERNING. But why? Were there guns in their other hands? I mean, there are things people are allowed to do in public that DO hurt others. Smoking is still legal.