“Fallen, fallen is Babylon the great, she who made all nations drink the wine of the wrath of her sexual immorality.”
It’s not enough for the chronic sinner to quietly sin in a corner. Whatever tattered shreds of conscience he retains will trouble him just enough that he must rationalize his behavior, and that requires seeking the validation of others.
To secure their approval, he needs them to be thinking the same way he does. The quickest way to pervert their intellects along the same lines as his own twisted reasoning is to introduce them to his favorite sin, so they can experience the very same sort of moral tension with which he is struggling. So the sinner in the corner becomes the cause of stumbling in the public square, and sin spreads. Maybe if everybody’s doing it, it won’t feel so bad.