The response to dishonesty should not be more dishonesty, but a model of correct behaviour.

I disagree. There was leverage to balance the sheet. The room mate was trying to steal money from him. Say anything that is legal to get it back and barring that get the cops involved (a last resort since that greatly complicates a situation).

Then assess the situation. Bad behavior shouldn’t be rewarded. There’s no reason the room mate should ever know how the parents learned that information. If the parents were tactful they would use the information to make a plan to bring it to light organically.

That guidance, often framed in religious terms, is a core tool with which sociopaths in power neuter their opponents.

I was happy to get out of there. It's not like I could have reformed them with a good heart to heart talk. Once I went to do laundry and stepped barefooted into a steaming pile of dog poo their dog had dropped on the laundry room floor. When I complained, instead of apologizing for it, they told me I should have watched where I was walking. My roommate was a genuine asshole, and just getting them out of my life was amazing.

Hmm, I seem to have worded my comment poorly? The comment I replied to suggested you should have outed them to their parents while living with them.

I was arguing that would have been an insane thing to do, as you would then have had no more leverage, and would have angered an immoral person.

I.e. You didn't need to do anything more than you did.

Ah, yes. I agree with this.

The anecdote was about getting back the security deposit after moving out.

> When I had had enough and moved out, they wouldn't return my security deposit.

None of it would have been safe to do if they were still living with them.