On the one hand, I can agree with you. I don't see someone managing to fake 1000s of votes by walking in without identification. That would require a lot of manpower, I imagine. On the other, I think you or I would still be pretty annoyed if someone had walked in and voted for us.
I would be much more annoyed if I found out that state legislatures across the nation were actively trying to make it so that tens of thousands of people can't vote. I would be especially annoyed if the people affected were overwhelmingly the segment of the population who is least able to fight such efforts due to their lack of resources and influence.
Of course I don't have to _imagine_ this scenario, because it happens every year.
Real harm, happening right now vs an imaginary harm that happens so rarely we essentially have to guess what form it would take... this is an easy one.
(re: guessing what form it would take -- if we're going to imagine a fake voting threat, we can just as easily imagine that these same people have the capability to get fake licenses. That happens _all the time_, after all, in college towns across the country. Amazingly these people seem to all use their fake licenses to get a drink, and not to go vote illegally for other people. Silly them!)
If that happened, you could still file a provisional ballot. If you succeed in proving your eligibility to cast a ballot (and that someone else improperly voted in your place), your provisional ballot will be counted.
This is one reason we know that in-person voter fraud is rare: because there are very few provisional ballots filed due to impersonation.
