He's shown me results of his monitoring and it pretty much ended the debate. Weird old guys contacting his son, excessive cyberbullying, swearing (fine by me, but still), being drawn to the wrong kind of "friends", hate speech, general addiction and obsession with games and in-game items, the list goes on.
Doesn't mean one should intervene all the time, but you should know. I'm not a parent so I don't know at what age you should back off, but I'd say don't do it too early. Your trust is misplaced.