I get what you’re saying, and I know you’re asking in good faith, but I feel that it’s going in the wrong direction. Voter fraud is not a common issue in the US; voter suppression is: voter roll purges, voter intimidation (like ICE at voting precincts), voting restrictions based on demographics, lack of a federal voting holiday(s), etc. Basically, voting is more secure than it is available.

Why can’t a simple fingerprint scanner be used at the polls?

My dude, all you really need are people who want free and fair democracy. America as a whole, doesn’t.

This is why you gerrymander, hang your chads, restrict based on ID, use easily compromized voting machines, have judges determine elections, reduce polling stations in blue areas and make long line ups with no time off work and an endless line of similar fuckery.

America is not a democracy. There is no technical trick that can fix bad faith actors.

Identity is hard. Biometrics do not magically make that easier. In fact, it brings its own problems. But before you talk about authN first think about enrollment and recovery. These are the hardest problems with any identity syatem.