He's a non-threatening insider, that's how he gets these guests. For better or worse, the titans of Silicon Valley don't want to be challenged, so they seek out or start their own safe spaces.
Hi! I'm starting a podcast where I interview totally random commenters on HN and ask them uncomfortable, hostile questions with the intent of embarrassing them in public. Would you like to be my first guest?
No he challenges his guests, he's just not an ass when he does. E.g. see his Jim Keller interview, when he disagrees with Keller when Keller talks about machine learning. And after a couple minutes of back and forth Friedman just lets it go by saying 'yeah we'll just agree to disagree' and moves on instead of making it personal or drawing the point of contention to a long hour because you have to be right! (as some of here may be guilty of doing :))
