According to Greg Palast: "The federal government reports that 300,000 voters were turned away from the polls in 2004 for lack of "proper" I.D. Not lack of I.D., but lack of proper I.D. In New Mexico, for example, voters who excluded their middle initial on their driver's license but included it on their voter registration lost their vote. But not everyone is asked for I.D. Experts for the US Civil Rights Commission calculated that a Black voter is 900% more likely to have their ballot left uncounted than a white voter."
So without introducing a uniform, mandatory federal ID card that is deliberately matched to the voter registration, ID card checks can -- and no doubt will -- be used a tool for dodgy vote challenges. The ID card also needs to be difficult to forge, or else it'll be useless at stopping illegal immigrants.
300,000 reported cases of improper ID taking away votes, versus Johns Hopkins' 1,500 dead people fraudulently adding votes: both are wrong, but it seems that only the dead people are going to be addressed by the current bill.