The US is the only country that I have passed though where they feel the need to poke around with your baggage that is in transit. (Its on my list of "shithole" countries).

I understand that one needs to go through customs & immigration, even if one is only in transit. But the idea that one needs to hand over one's "diary" is beyond me.

It's my understanding that a lot of US airports don't have an international-only terminal where people in transit wouldn't have to first go through customs & immigration.

Quick google search brought me here: https://www.tripadvisor.com/ShowTopic-g1-i10702-k10297825-Do...

No airport does; you are required to clear the US border to connect. There's not such thing as a transit passenger in the US.

Well, actually... There are.

LHR-LAX-AKL requires all passengers to get off but those not terminating in LAX stay in a transit area (although there's still an immigration check).

And IAH supports international transit for bags, but you as a person still need to immigrate the normal way.