Loyola University law professor Justin Levitt tried to quantify the epidemic of voter ID fraud that's forcing so many states to pass restrictive voter ID laws. He looked for not only cases where someone was convicted, but tracked "any specific, credible allegation that someone may have pretended to be someone else at the polls, in any way that an ID law could fix."

Out of roughly a billion votes cast, he found 31 credible cases of voter ID fraud. And that is, he thinks, an overestimate. At the same time, thousands of people really are being turned away from polling places because they don't have the right ID. So voter ID laws fix a fake problem by creating a very real one.

Which isn't to say voter fraud isn't real. In an August interview on MSNBC, Levitt explained why the voter ID laws don't do anything to address the main kinds of voter fraud:

It may not seem like asking for an ID is a big deal, but as Jenee Desmond-Harris writes in her excellent overview of voter ID laws, the numbers say otherwise:

A full 11 percent of voting-age US citizens — about 21 million people — don't have a government-issued photo ID. That means, in states that have strict photo ID laws, they can't vote. Racial minorities are disproportionately likely to lack photo ID and make up a big part of that 21 million. Fully 25 percent of African Americans of voting age (compared to only 8 percent of their white counterparts) don't have a photo ID. Voter ID laws also have a disproportionate impact on low-income Americans, who are less likely to have driver's licenses or to be able to afford a form of identification, which can also be used as ID. According to a September 2014 Government Accountability Office report, fees for driver's licenses range from $14.50 to $58.50. These are not huge fees, but they're certainly significant if money is tight. Even for those who could afford it if they stretched, $50 price tag on voting could be enough to dissuade them, which is its own form of voting restriction.

And that's to say nothing of the time-cost of getting a photo ID, which may require someone with two jobs, three kids and no car to spend hours in the middle of a workday at an inconvenient government office waiting in line to get the ID. When you make it harder to vote, fewer people vote. That may be worth it if there was some huge epidemic of voter ID fraud. But there's not.