The letter promotes a helpful, but insufficient, solution for election security.
I support paper ballots for all the reasons the letter describes. Auditable paper ballots, however, only protect the integrity of the vote-counting process. They do nothing to ensure the integrity of a voter registration database. For that we need positive voter identification, such as photo ID, to prevent fraudulent voting.
The reasons for voter ID are the same as the reasons for the paper ballot, just applied to a different part of the election process. To be eligible to register to vote, persons must prove their identity. But, subsequently, the registration record is vulnerable to hacking and modification. Repeating the identification check at the polling place is a way of auditing the registration records.
It is, in fact, the best way of auditing them as a technical matter. It should be done as a matter of routine.