It establishes both trust by separating it from mistrust (paranoia if you will) by making the division explicit and assigning trust to some people and operations and not others.

If you think it's concerned about screens, you're wrong. It's concerned about "did this person really do this"?

Do you understand that you are trusting your screen?

Do you also blame the post office when someone breaks into your post box?

Can you build a post box? Can you build a computer and the software?

A screen isn't software. And indeed, I can't. There are specific parties concerned with building postboxes and screens, and those have no reason to be the same as those delivering mail or writing blockchain software.

I mean you might as well just throw out all computers then.