* A good barista will have no problem customizing drinks.
Note that I didn't say impossible. Just difficult. You can probably get to better-than-Starbucks quality without too much AI. Auto coffee shops that beat starbucks already exist. But I'm not aware of any auto espresso machines that can compete with the baristas at my local coffee shop. And even if they could, I'd probably only use them at work, at airports, and at hotels.
> but having a proof that humans can reason through from beginning to end makes people feel more comfortable.
Saying that humans can't reason about computer-checked proofs is like saying humans can't reason about source code; which is to say, it's obviously false in the general case.