Personally, my concern is that with mail in ballots some nutjob that believes there's ballot stuffing can set fire to the ballotbox and even though they're caught it's a major inconvenience to get a replacement ballot and the websites that show your ballot is received take days to update.
But I still love mail in voting. My state sends a candidate brochure with it and I can take my time to actually look up all those random candidates' policies. It takes me hours to actually fill out my ballot but that's a feature, not a bug (there's nothing preventing you from along party lines but frankly I'd be happier without parties)
[1] - https://www.brennancenter.org/our-work/research-reports/voti...
If thousands of people were told "you already voted" when they showed up, then that would be very very obvious.
They also really do look at signatures and contact voters to cure ballots if they're unsure.
[1] - https://ballotpedia.org/Election_results,_2024:_Analysis_of_...
Hell, the fact that so many people have been looking for massive voter fraud for about a decade now and haven't is pretty telling. People aren't good at keeping secrets and if it's being done at scale it would be uncovered or leaked. Accidents and stupid people happen, but that works both ways
This is why many of the election fraud claims focused on lax signature verification of ballots as well as the lax mail in ballot address locations. I feel that IL elections are probably more secure, but only because the state is solidly one party and comically gerrymandered anyways.
But technically, yes, a ballot harvester could send ballots on your behalf if they have enough information about you.
But you can already do that, regardless of mail in voting or not?
Not to mention the peer pressure. What asshole is going to stand in the booth for hours voting? I got to get to work!
Sure, you can do all this at home but there's a clear convenience when having both in hand