The bible was not the first authority that considered murder and theft wrong

Though the US founders may have made them illegal based on biblical beliefs, the overall moral belief came from before that. If God makes everyone with equal worth, then why are straight people the only ones deserving of having a happy marriage with the person they love? Also, why would homosexuality be harmful? It's simply two people who love each other and happen to be the same gender, and it isn't personally affecting anyone who doesn't agree with it, so I don't see why it would be an issue.