The voting period in Washington is 18 days. So someone would have to either be constantly looking through my mail for the better part of three weeks, or have the best luck when it comes to predicting when I would actually send it out, and that's if they got the correct mailbox and I didn't, say, go to a post office or the ballot dropoff boxes. It would be hard to do even for an individual, and much harder to scale up.
It’s difficult to scale without getting caught.
The US currently has digital (often internet connected) polling booths, which bring all the security problems of mobile/net voting, and none of the benefits.
I would much rather have mobile voting, as opposed to the current widespread digital voting booths system. Ideally, of course, we'd want to go the paper ballot route for now.
I have no confidence in any mobile voting scheme, and for an election, lack of public confidence in a process should be immediately disqualifying for said process.
Maybe mail-in ballots could come with QR codes but this kind of defeats the idea of a mobile-only option.
Maybe we just need to accept that some voter fraud will happen like it already does (the standard for voting in-person is nothing but matching the name you tell them to a list of names, not even any ID required) and settle for something potentially exploitable like SMS's with links sent to phone numbers whose registered names/addresses correspond to a registered voter, where you then have to verify some information like past addresses or whatever. If we'd just force telecom companies to tighten up their security that would be a perfect solution, and as it is it's probably good enough using the existing rate of voter fraud as a bar. Stealing a phone number in the process of identity theft is something that happens and is easier than it should be but it still takes a while on the phone and someone making a full time job of it just to hope to catch that automated text probably wouldn't get that many, if the texts were sent at random times throughout a whole month or so.