Why is Sin Such Damned Fun?

Hieronymus Bosch,The Garden of Earthly Delights (1510)

We’re about to enter into Good Friday, the day on which Jesus died for our sins. So what’s the deal with sin? It’s very easy to think of sin as fun, and virtue as sort of missing out on the fun for the sake of some future reward: a sort of Mardi Gras v. Lent contrast. Why IS such (literally) damned fun? And how do we respond to the charge that we’re just anti-fun?