You have to trust the voting place/ballot receiver in all cases. Like, after they take your name, you need to make sure that they aren't secretly associating your name with the ballot you are filling in. Likewise, if you vote by mail, you need to make sure that they aren't associating your identity on the envelope with the anonymous ballot inside the envelope.
That only solves the double-counting problem, and it's fundamentally impossible to solve the voter ID and voter manipulation problems with postal voting.
I'm not American, so I don't understand the older republican comment, but except in exceptionally adverse circumstances (astronauts on the ISS or submariners, etc) the military can provide ballot boxes to it's personnel.
Military and overseas voters vote in their home state elections, even federally (all elections are held by states, even for federal candidates). You would need to ensure that there is a ballot box representing each state that has an eligible voter at a given site, and then need to figure out logistics for getting thousands of sealed boxes back to the vote counters in each state within the allotted deadline. You would also need to solve the issue of maintaining vote anonymity at low volumes.
Or, you could have a central, federally run organization that takes responsibility for delivering sealed ballots to the respective states in a timely manner. Which is what we call voting by mail.
> Or, you could have a central, federally run organization that takes responsibility for delivering sealed ballots to the respective states in a timely manner. Which is what we call voting by mail.
No, postal voting is not the same as bringing ballot boxes to voters in exceptional circumstances and does not have the same set of tradeoffs. Postal voting in particular certainly does not solve the voter manipulation problem.
The fact that so many other countries manage to actually provide ballot boxes to all voters, even to voters in much more remote scenarios than US military service and countries with far fewer resources means that the US has no excuses.
They use mail in ballots. Older people who are seen as having trouble reaching the polls can also vote by mail in most states. American conservatives don't see these as problems because these mail-in votes are generally in their favor.