If not for compassion or punishment, why not be a selfish bastard?

Please curb any purely emotional responses in this thread, they’re no help here. Thank you.

Here’s another ideological problem I’m struggling with.

I’ve been haunting Omegle for a while now. It’s an anonymous chat site that pairs up users at random.
A few days ago, I ended up talking to someone who collected child porn. A guy who openly didn’t mind contributing to child abuse, who admitted he “would happily encourage someone on webcam to abuse a child for [him] to watch”. Who only cared about not getting caught. Simply put, a heartless bastard without a conscience.
An intelligent and reasonable man, too. He conceded any reproaches I flung his way, he was very willing to hear me out on whatever I had to say about why he should change, and he calmly and apparently open-mindedly examined my every argument.

And I eventually found myself running out of things to say.

Compassion? Responsibility? Conscience? He didn’t care. Nothing there to appeal to.
Self-respect? He had no problems with himself.
Getting caught? He was careful enough to get away with it.
Divine judgement? He didn’t believe in that. (And neither do I.)
Human judgement? I pointed out nobody will ever truly understand him and love him at the same time in this situation, and that anyone who knows the truth about him will hate his guts. I’m not sure to what extent he cared about that.

Perhaps this is my cue to abandon the notion that reason can solve any problem it can reach. Perhaps the only thing one could do is forcing one’s own sense of right and wrong on people like him. Even if they are willing to listen to reason, and you just can’t refute their position.
And I find it hard to think of this as a lesser evil.

What are your thoughts?