What's wrong with incest?

It seems we've been socially conditioned to view it as wrong and sick. But, why is that? I once had a crush on one of my cousins. What's so wrong and gross about that? Some people even consider it wrong and sick to be attracted to a step-sister or step-brother, who wouldn't even be blood-related. People confuse me.

I'm pretty sure inbreeding is discouraged because it damages the genepool. Most people probably do not want to be responsible for regressing genetic progress.

Do humanity a favor and improve the genepool, marry a black person.