Sam Harris is a globalist, pure and simple. He likes globalism. He actually had a guy on where they discussed how to make globalism more appealing, and how to get rid of any negative connotation it had.

It seems like he's a highly intelligent man who is still ideologically possessed by narratives that are being spoon fed to him, or worse: are a part of his self-identity now.

I've seen it a few times in academia, by people who I would say are genuinely brilliant, but still manage to be leftists. Sometimes it's an identity crisis issue where someone demands to hold onto a label as part of their personality, and sometimes they've mapped a narrative onto their perspective. That last one is particularly tricky, but I normally see it in racialists who see everything from the Racial Theory of HIstory. You'd have to shatter both their self-identity and their narrative perspective of the world to get them to think outside their own narrative limitations, which is very hard without significant personal exposure/experience. Effectively, they have to be deconverted. Unfortunately, Harris knows exactly what a deconversion is, and how hard it is to go through for the person deconverting.

Another part of this might be that highly intelligent people are easy to manipulate when it comes to authoritarianism. The kind of Technocrat fallacy. "Because I'm a smart person who is normally right, it must mean that I know what the right thing to do is for everyone else." If you're a literal genius, and everyone around you appears genuinely less intelligent than you, you could easily fall into the trap of assuming that you know what's right for them, because you're so often right about other things. It builds a bit of an ego that they might not actually know how/when to control.