By what you say murder is not wrong, it just means that if you murder than you will be murdered. Adultery is not wrong, it just means that if you lust after someone, someone will lust after you. If you cheat on you wife, she wil cheat on you. Having sex with someone before mariage isn't wrong, it just means someone else will have sex before marriage. That makes no sense at all to me.
I do not trust intuition. As an unbeliever every intent of my heart was evil, against God, and striving for independency from Him. As a Christian I still have a sinful nature that is at animosity towards God.
I would say that homosexuality has at its root idolatry. The love of sexual fulfillment more than God. And not to be an idolater is the first commandment.
We are moral creatures. Everything we do is either right or wrong, even going shopping and chewing gum. It is morally wrong to sin. Why? Because God is Creator and thus deserves total obedience. So no matter what God says, to disobey is to be immoral. Now it ends up being that God has reasons for all of His laws (atleast I've never found one that had no reason) Examples are do not commit adultery to eliminate abortion, divorce, anxiety, mistrust, betrayal, and disease. Do not be homosexual to avoid disease, no offspring, improper place in society, improper treatment of the other sex, etc...
Perhaps Jesus said it better (No, I'm sure Jesus said it better) when he said, "And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.