Yes, it has to be. If you break the ability for the average citizen to understand exactly how and why your vote is counted, you undermine trust. Trust into the democratic process is the thing keeping a democracy alive.
If someone currently says "<Country> / <Party> interfered with the voting process!", I can tell them to just observe their local polling station or even become part of the polling station staff themselves. Be there, check that the election staff doesn't start throwing away votes and count correctly. Check that the numbers they count are equal to the one on the official result for the polling station. It's all paper. It's easy to follow.
If we put anything between this, which requires trust into a magic box with a display, I cannot do this. If your credit card is abused, you see it on your bank account, always. You cannot have the same certainty the same for an anonymous election - yes, they may have proof that their vote was correctly counted, but what about the polling station as a whole? The votes of the other citizens? Most people will not check, just as you may only get one observer per polling station max today (which is already enough to prevent fraud for the whole station, in the case of paper ballots).
"Trust the journalists" does not fly.
> And remember, physical voting is actually tremendously complicated as well
It doesn't have to be. You don't need complex equipment, you can count directly in the polling station after it closes. Paper and people suffice.