Did the study document what type of irregularities they could have missed? It is like claiming I have never been hacked because my logs never showed anything.

Did the study document what type of irregularities they could have missed? It is like claiming I have never been hacked because my logs never showed anything. If you really want to look at the issue, you need to approach it like a security audit. What is your threat model? What are the failure modes? What are the ways that there can be fraud without setting off red flags. Right off the bat, an issue with all-mail elections is coercion, and suppression. If the ballots all arrive in the mail at the house, someone can use coercion to make sure all the ballots are filled out as they wish. This is much harder to do in person. And that vulnerability popped up with less than a minute of thought. If approached from a security perspective, I am sure others would pop up. Now, after serious analysis, it may be concluded that the benefits outweigh the risks, but a serious analysis needs to be done.