I've got over a decade of experience supporting elections using a ballot scanner.
The need to balance voter security, with auditability, rapid Ness of results, with ease of setup/teardown of the voting place, is hard to beat with scanners.
> Hand-counting the ballots instead of scanning would be expensive in terms of time and money, and error-prone.
Why?
It's not that expensive - what price democracy? And in terms of error rate - if there is a very close vote, in the UK they just do a recount - sometimes more than once - the variation between recounts is very very small - single digit ( votes not percent ) at most.
to be fair, I guess one difference between the US and the UK is the distributed nature of the vote - in the UK it's broken up into constituencies of ~70K voters - so any recount is scoped to that ( ~ 50K actual votes ).
For a non-trivial amount of ballots, the overhead of securely managing the ballots is substantial. You're casually driving up staffing costs all over the place, and legal challenges will ensue if everything is less than meticulous.
Extend the question why are rapidity of results and ease of setup/teardown of the voting place design goals at all?
There are elections in India and the US to control billions of people and some very aggressive military people armed with weapons capable of ending modern civilisation. This is one of the most fundamental social technologies we have to keep the whole system stable (up there with limited liability corporations and courts). The downside of one of those elections failing because of voting machine trickery is stupendous.
Frankly, I'm not sure even auditability is that important as a design goal compared to voter security. If the election is close enough that an audit matters the two candidates are pretty similar. In practice, if there is any meaningful gap in preferences then the outcome of the election should be clear enough that an audit isn't that meaningful. It's nice to have and it is cheap enough to include in a paper ballot.
The last 3 US elections were very close and had very different candidates with very different ideas. The closeness of the election has nothing to do with the “similarity” of any candidates. And to imply a “coin flip” would be fine is ludicrous.
Even the next day is silly. If the election is Thursday, it seems reasonable to count on Friday and the weekend, and have the new MPs declared on Sunday, ready to travel to London on Monday and get sworn in.
In the US, the election is in November and the president doesn't get sworn in until January. It could take a couple of weeks to count the votes and it would be fine.
The need to balance voter security, with auditability, rapid Ness of results, with ease of setup/teardown of the voting place, is hard to beat with scanners.