There are a few sins that really give me some concern. Most sins are morally wrong because they cause social harm. That is very understandable. If something can cause someone harm then it should be immoral. However, most sexual sins don't seem to cause social harm except for when a spouse commits adultery and rape. Since there is no social harm then I wonder why they are considered morally wrong.
Is sexual lust morally wrong? Let's look at this. Everyone has seen someone who turned them on. Can humans honestly control their hormones to the point they cannot get sexually turned on?
Another issue is homosexuals. Is being a homosexual causing social harm? Not really. If two men or two women are having sex(assuming none are married) then no one is being harmed in any form physically, mentally, nor economically.
Is watching porn wrong? Again assuming the viewer is not married. No one is getting socially harmed.
Is paying for sex wrong? If the customer is not married then I don't see the problem as long as protection is used.