He could not be more right. Voting is meant to be anonymous for a good reason. However, that makes it extremely easy to cheat. The only chance you have at stopping it is via an open and transparent election and catching any cheaters in the act, because the audit trail is extremely weak. Verifying signatures is one post process control that you can audit, but after the election, the true ballots would have been destroyed and the fake ballots would have been put in their place with zero ability to separate legit and Illegitimate ballots. Their behavior on election day is enough to conduct a transparent revote.