It's not that difficult to prove that voter fraud is extremely rare. Allegations of voter fraud (one person attempting to cast a vote under someone else's name) are made quite a lot, and almost none of them turn out to actually be legitimate cases of voter fraud. They almost always turn out to be cases of human error or two people having the same name and birthdate, or people voting by absentee ballot before the election and then dying between the time they send in their vote and the actual election day.

On the other hand, election fraud, one example of which would be purging the voter rolls illegally as has happened in recent elections, is a real problem and has resulted in large numbers of people being disenfranchised.