It’s a common trope that atheism is a form of belief. It’s nonetheless misinformed. It’s often trotted out by people who have a religious belief and are unable to comprehend that large numbers of sensible people are able to exist without holding any religious belief, yet call themselves atheists. I gather that you are not one of those religious people but you seem to be using their argument.

Again, the belief at discussion here is not strictly religious or spiritual. I accept that totally normal people can live totally normal and fulfilling lives without any religious belief, and in many cases I think they, and the world, are better off for it. What I don't comprehend is a totally lack of belief in anything, even in the worldly or mundane or personal or scientific, because otherwise the human condition is just a big tangle of absurdity that we should all quietly exit from.

From later on in the speech transcript linked:

"Worship power, you will end up feeling weak and afraid, and you will need ever more power over others to numb you to your own fear. Worship your intellect, being seen as smart, you will end up feeling stupid, a fraud, always on the verge of being found out. But the insidious thing about these forms of worship is not that they’re evil or sinful, it’s that they’re unconscious. They are default settings. They’re the kind of worship you just gradually slip into, day after day, getting more and more selective about what you see and how you measure value without ever being fully aware that that’s what you’re doing."

I’m saying I don’t agree at all with the linked transcript, particularly the part you quote.

I don’t think this person has a lot of insight into the minds of non-religious people.

The part of your post reading “ agnosticism is more diametrically opposed to belief than atheism; the latter is belief in one's own disbelief.” is a misrepresentation of what atheism is. Atheism is the conviction that there is most likely not any higher being. Agnosticism is ”I’m not sure if there is a higher being or not”.

Conviction: a fixed or firm belief [dictionary.com]; a strong opinion or belief [Cambridge Dictionary].

Atheism: the doctrine or belief that there is no God [dictionary.com]; the belief that God does not exist [Cambridge Dictionary].

Also, "this person's" father was an atheist, he studied philosophy, and was in-and-out of addiction recovery programs throughout adulthood. He likely had more insight into the minds of non-religious, religious, and whatever people than you're giving him credit for.