I’ll lead off by mentioning that some states already voted by mail and have for many years. So if there were a problem with this approach that enabled mass voter fraud we would be well aware by now.
The “blank ballots” are not blank in the sense that they are interchangeable. Each ballot sent out is the specific ballot of a specific person. It’s certainly possible that some ballots were stolen from their intended recipients and mailed back with forged signatures, but what’s important is whether this could have been done on a mass scale to influence the election result. And the answer to that is no. A coordinated effort to fraudulently return enough ballots to matter would require large-scale raiding of mailboxes to steal ballots, or stealing ballots in mass quantity soon after they were put into the postal system by each state’s election commission. The former is impossible, as it would require an organization comparable in size to the postal service to be able to go house by house stealing ballots as they were delivered, and it would be obvious that it was occurring. The latter is easy to detect and trivial to rectify.
In both cases, the fraud would be detected as soon as anyone who hadn’t received their ballot went to their state’s election website and requested another ballot and were informed that their ballot had been delivered and returned.
I'll post this scenario here again just to get your opinion on it -- you have good thoughts.
Here's the scenario as it plays now: many 'grassroots' movements are reified when a bus comes to pick a group of people up, hands them a template ballot of who to vote for, then brings them to the polls to vote, and finally ends the ride with a dinner and party back at the place.
First, this is legal, at least where I'm from, and is a common way to 'get out the vote.'
Second, this implicitly has a built in rate-limiter because I need the physical voter to be present and to go into the booth alone.
However! This time, I don't have to bus you to the polls... I can host a party at my house to request all of your ballots come to me, where I fill them out and copy your signature from the party / event. OR I do this over the course of a few months, and still have all the ballots directed to me, still copy your signature from the form we filled out together. Or even worse, I use hacked data to request a ballot on your behalf because you never show up to the polls anyway.
To me, that's an extreme vulnerability -- that means beyond it not being rate limited, the physical person is no longer needed to fill out their own ballot. Not only this... there was always the chance someone could go 'off script' and vote for who they wanted for and just get the free meal. Now, they are guaranteed to be the way you wanted because you filled them out.
^ I've known people go on buses to get meals and vote 'off script'
And finally, the reason 'this hasn't happened until now' is because most mail in voting was for absentee voting (in the battle ground states) and never done at this scale where you could have a whole community request ballots to one address almost undetected. (yes this is detectable post-fact, but damage is done and intent is there on both sides.)
Oregon, Washington, Colorado, and Utah have voted by mail and sent a ballot to every registered voter for years. No signs so far that this has been abused to facilitate the sort of coordinated large scale fraud that you’re concerned about. Though there’s some evidence that it leads to closer matches between the votes of married partners compared to in-person voting, which is very concerning for for similar reasons! But spousal vote coercion is not new and by most definitions is not a form of voter fraud. I dream that someday we will be able to introduce a voting system that can ensure ballot secrecy even in these scenarios, but sadly the technology isn’t there yet. (Side note - this is why taking a picture of your ballot in a voting booth is illegal. It prevents being able to prove how you voted.)
Ballots are delivered to the legal address of each registered voter. A state election board is going to notice (and maybe call the fire marshal haha) if 1,000 people all suddenly announced that they are moving into the same house. The premise that neither the state nor the people having their legal address surreptitiously changed would notice isn’t a realistic cause for concern.
The “blank ballots” are not blank in the sense that they are interchangeable. Each ballot sent out is the specific ballot of a specific person. It’s certainly possible that some ballots were stolen from their intended recipients and mailed back with forged signatures, but what’s important is whether this could have been done on a mass scale to influence the election result. And the answer to that is no. A coordinated effort to fraudulently return enough ballots to matter would require large-scale raiding of mailboxes to steal ballots, or stealing ballots in mass quantity soon after they were put into the postal system by each state’s election commission. The former is impossible, as it would require an organization comparable in size to the postal service to be able to go house by house stealing ballots as they were delivered, and it would be obvious that it was occurring. The latter is easy to detect and trivial to rectify.
In both cases, the fraud would be detected as soon as anyone who hadn’t received their ballot went to their state’s election website and requested another ballot and were informed that their ballot had been delivered and returned.