The only thing Acorn was guilty of was ineptitude. Their volunteers were "paid" for every voter registration form they turned in, so of course the temptation to fill out forms with bogus information was irresistable. The registrars who got the forms saw through that, and the bogus names never made it on to the election rolls. It's disingenuous, and outright dishonest, to toss around accusations of voter fraud when that never took place.
As for disenfranchising, it's not any one particular instance, as we see here with Ms. Cooper who eventually found a way to be able to vote. But there are a lot of Americans in similar circumstances who don't have the time or the support network in place that allows them to persist until they get what they need to exercise their voting right. The law is designed with these Americans in mind - anything to put yet another obstacle in their path, in the hope they'll just give up trying.
I imagine a lot of the folks in this thread who are defending the picture ID law are typing from the comfort of their suburban homes, not thinking twice about the two late-model cars in their garage that enable them to get around without thinking twice about it, and being able to do so during their "leisure time". Compare that to a minimum wage earner holding two (or more) jobs who relies on public transportation for whom "leisure time" just doesn't exist. They're not likely to be GOP voters, so if there's fraud anywhere, it's being committed by those who support these kinds of laws and perpetuate the fear behind them.