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!)
This is one reason we know that in-person voter fraud is rare: because there are very few provisional ballots filed due to impersonation.