I think the theme is more along the lines of, he knows intellectually that Elizabeth is lying but she triggers authentic emotions of trust and sympathy. He's smart enough to not let his emotional reaction override his intellect but he's fascinated at the cognitive dissonance.

It's similar in style to The Rehearsal, he shows you how Elizabeth can manipulate people by example instead of just talking about it

I mean, these people did buy her lies, so clearly they are not so good at figuring out what to believe.

The number of people who don’t understand the film is truly staggering. We need to fund education in this country for better media literacy if nothing else.