https://www.youtube.com/watch?v=w3_0x6oaDmI
Here's a video that says it better than I ever could. I'm not well versed in this area so I try to keep my statements to a minimum.
I like the efficiency idea, but I remain totally unsold on privacy and security concerns.
Pretty good video, here are the problems he summarises.
1: Auditing the software and hardware
2: Transit of voting data
3: Central count program with little to no accountability
I'll try and approach this from a standpoint that electronic voting has to just be better than paper voting, not impeccably perfect.
Problem 3 is easily solvable, who said the implementation needs a single central count program? Distribute the data from all machines to multiple (could be hundreds to thousands if necessary this is totally trivial) systems held by mix of the stakeholders of the election. Data has to obviously match between all counters to be considered valid. This is actually a really dumb solution and could be done with much more complex security measures but with the same underlying principle, it ensures against corruption of a central count program.
Problem 2 is mathematically solvable thanks to quantum key distribution technologies, transit of data is not an issue. Also note QKD systems are not quantum computing systems, they can be implemented with commercially available technology right now. But there are some vulnerabilities with modern systems due to hardware imperfections, these will be solved in time. QKD systems are also vulnerable to man in the middle attacks to the same extent and classical communication protocol is. But it is possible to authenticate using unconditionally secure schemes designed for QKD.
Problem 1 is hard to solve. At least to my knowledge. I'm sure smart people can think of a way to at least make it as secure as the paper counterpart.
Also paper voting is very vulnerable to MITM attacks. Like every step of it. Vote transit, vulnerable. Calling in results to a central count, extremely vulnerable. Pencils? cmon man.
The best argument in favor of paper voting IMO is that it's very easy to commit small scale fraud, but complexity raises immensely as you try and increase the scale of the fraud. With electronic voting it would be extremely difficult to commit small scale fraud, but if you can change one vote then you can probably change much more than one.
Also as a note. I don't support electronic voting because it's faster, but because I genuinely think it can be much more secure than paper voting.