It would seem that Mike's take-away from that was not learning the integrity he was supposed to have learned. His juvenile and nasty attack on the Kelpfroths was okay in his eyes because he'd learned never to let the sucker find out. What Dummy didn't want to realize is that even if his victims didn't read the magazine his slurry of ad hominem attacks occurred in, it didn't mean that they didn't have friends who did. His lack of knowledge of people in his way taught him a third and worse method of pilfering from other peoples' lives: making things up.
This is why we have what is probably an author insert stuck in the middle of Stone Season. Mike's drug fiend reasoning appears to have been that since there was no such person in Mrs Dingle's past as Mystery Scandinavian Dude, she couldn't sue his ass off for misrepresantion.
What interests me is that all three of Mike's techniques have a real-life inspiration: a back-poking snake of an author who sees the people around her as fodder for her gibbering.