> Public doesn't need to know the details. Production of paper, printers is quite complex and so production of the pen. Yet people are not concerned about that when voting and we don't publish schematics of a printer that printed the ballots.

Except that people know what paper looks and feels like, they know how it absorbs ink, they know its various properties, they can _read_ whatever is printed on them, and they can see that the marks they make (or a ballot marking device does for them) are faithfully visible on the paper. With paperless machines there is nothing comparable.