Tim Lee has tweeted that "voting by mail is a huge privacy and security risk, and states should be discouraging it a lot more." He elaborates on his blog:
Imagine if an employer, who everyone knew to be a Republican, required his employees to request absentee ballots and show them to him before they were submitted. Think of an abusive husband who insists that he and his wife fill out their ballots together. Or imagine a political operative going around a low-income neighborhood paying people $50 if they let him fill out their ballots for them. This kind of corruption is very hard for voting officials to detect. And more insidious, voters themselves may not even realize that it’s unethical.
Now, there are some circumstances, such as soldiers stationed overseas, where absentee voting is unavoidable. But traditionally, to get an absentee ballot you had to give a specific reason that you would be unable to make it to your regular polling place on election day. But in the last couple of decades a growing number of states are dropping these restrictions, allowing anyone to vote by mail without giving a reason. And the states of Washington and Oregon are moving towards mail-in voting as the default option. Although this is moderately more convenient for voters (and election officials!), the effective abandonment of the secret ballot is too high a price to pay.
I worry about this too. There's also the issue of losing a collective decision at the same time on the same day. Things change, events occur, the world moves. It makes sense to me that an electoral decision is more coherent when it is made simultaneously over a single day, than stretched out over weeks or even more than a month.