If, as I wrote yesterday, God loves everybody, why does He speak negatively about homosexuality? The same reason He speaks negatively about adultery, fornication, abortion, and every other perversion of marriage – it’s harmful behavior.
Perversions of marriage are not just harmful to those who commit the perversions, but also to society. Therefore, God condemns as sin every violation of the sanctity of marriage.
By the way, if you don’t think abortion is a perversion of marriage, then you don’t have a biblical appreciation for what marriage is. If that’s the case for you, I encourage you to read the book The Honor of Marriage (click on Books in the menu bar above).
God is against sin for the same reason you are against little children sticking their fingers in electrical sockets. A little child sees nothing wrong with it, but an adult knows better.