If I were to go and vote as John Doe there is nothing to prove that I am clearly not John Doe. If ID was required it would ensure that everyone is who they are claiming to be. This helps keep voters from both parties in check. This also can help ensure that neither party has an unfair advantage over the other. Do denounce voter fraud is to effectively say that certain people do not lie to gain an unfair advantage. Sure, in a perfect world we would all vote as ourselves but we cannot trust everyone.
Voter Fraud is and issue that plainly doesn't exist. Only 31 cases of voter fraud have occurred since 2000. There is no need for Voter ids and the fact is that Voter IDs haven't stopped a single act of voter fraud since these laws began being implemented. It just ins't happening.