Ballot secrecy. Without it you get vote-buying and voter coercion. If you want to see what that looks like, ask your legislators about which lobbyists they met last week.
There's also people providing their public address as proof of a vote in exchange for something, but the risk for the buyer is that someone just hands over someone else's transaction and votes as they please.
A real potential solution would be to make the votes private and "untraceable" (A la Monero ring signatures or something of the sort), but that kind of comes with it's own pros and cons and could always be broken later. I still think it's worth investigating if this is more secure than plain old paper ballots.
Cryptography is powerful, but it tends to be on such an absurdly higher level of assurance inside its narrow applications that it becomes very attractive to try to stuff everything into it, whether or not that's warranted or useful.
Democratic legitimacy comes from the volume of participating individuals who trust and understand the system. Paper ballots are easily understood, independent electoral commissions improve trustworthiness, election scrutineers ensure every room has mutually suspicious observers highly motivated to detect problems, compulsory voting helps ensure the median voter dominates policy and preferential voting helps prevent minority candidates from inverting majority preferences against bad candidates.
None of these require a blockchain. It is a distraction from the actual reforms that will make the important differences.
The kind of electoral systems most of us want requires both ballot secrecy and a trustworthy count. Pure software ballots don't achieve that. Paper ballots don't categorically achieve it either, but it's much harder to violate either of the secrecy or count requirements because paper is bulky and the watching eyeballs are numerous. In practical terms: paper ballots can be made to work. I'm from a country where they do.
A blockchain system either works on a public chain, meaning I can sell my vote, or it uses a zero-proof scheme. The zero-proof schemes I'm aware of require someone, somewhere, to seed the chain with a private key. Then we're all just supposed to hope they deleted the one set of bits that can untraceably edit everybody's history. They pinky-swear they'll do it. But there's no way to prove they did, which rather sours the blockchain-can-prove-anything story.
Not to mention the problem that they allow retrieval. Sure, you can't prove that I ever owned a particular ballot. But I can retrieve an identical ballot. That might work for evading money laundering charges but it still kinda fits the vote-selling usecase.
It drives me nuts because this our love of reinvention and our fondness for assuming we can solve everything from first principles as if nobody's thought of these problems before. These problems are already solved in a simple, scalable, subversion-resistant way that everyone can understand. All we have to do is accept that, for once, our profession was not required to interrupt everyone else to give our opinion.
I am being dead serious and I'm not trying to antagonize you here: the fact that you responded and seemed to have a firm opinion on an area you admit you aren't well versed in... well that to me is a huge problem with the way democracy works. It's a trait that we complain about when non-nerd voters vote in uninformed ways on technology and science issues. Blockchain isn't going to solve that.
Better educated voters will do a lot more to improve democracy than blockchain will.
We can't even get reasonable technology choices for the evoting approaches we've tried (we can't even get vendor transparency), and that's not for lack of good proposals for evoting systems over the years. It's because the people choosing the technology don't understand it super well, and are often in the pockets of the vendors.
In practice, it feels like paper ballots are a much better solution than most of the evoting systems we use in the real world currently, and paper ballots certainly feel better to me than any of the completely nebulous "but what about blockchain?" proposals here and elsewhere.
to anyone still harping on blockchain, can you give a detailed description of a realistic threat model where it performs better than paper ballots.
>>> I still think it's worth investigating if this is more secure than plain old paper ballots.
I would agree with that general sentiment, but the overwhelming evidence right now points to "no", IMO.
i will also say, the thing that you're doing that i'm complaining about is a thing that programmers do a lot, and is a thing that i'm plenty guilty of myself (thinking everything is more solvable than it is because you can envision rough pseudocode or systems diagrams for it in your head). this is a thing i'm really trying to get better about not doing.