Here’s the part in Slate that’s most objectionable to me:

Second, the (still relatively rare) instances of voter fraud to which Hasen alludes likely would not have been foiled by a ballot selfie ban. Vote-buying almost always occurs through mail-in absentee ballots, not at the polls

Uh, this misses the entire point. The reason vote buying takes place with absentee ballots but now with in person ballots is because the secret ballot prevents verifying how one voted, thereby cutting down on effective vote buying (and coercion from spouses, employers, etc.)

Provide the way to verify the transaction and the very same danger is likely to reemerge. I have no doubt.

And the civic virtue of taking a picture of the completed ballot compared to a selfie in front of the polling station seems to me to be exceptionally marginal.