It's unlikely that you're actually familiar with his work.

There are many examples of videos like the one below, and if you'd seen any of them, you would absolutely understand why people think this.

https://www.youtube.com/watch?v=n-X0YD0tYTw

I've literally seen this before but thanks for telling me about yourself

If you've seen this and you don't understand why people think he modeled constructive conversation, I think that says a lot more about you

I think this because I saw him go on a college campus, give a microphone to liberal students, and give them a chance to defend their views while also providing an alternative point of view.

Can you explain why you’re flabbergasted?

Because you are able to watch a carefully staged piece of theater and mistake it for reality. I thought most people, in general, were able to discern the difference, but you and many aren't