At the risk of being flamed, I'm in favor of using driver's licenses as Voter ID/registration. For those who don't drive, every state offers a photo ID.
At least there's some consequense of having a false driver's license, and there are databases that can be checked instantly to prevent duplicate voting. Also, the address used for a license can be checked against the post office database of valid residential addresses.
You can have both the rule of law and easy access to voting.
This is where that whole slippery-slope thing comes in. Drivers' licenses have been defended up to now with the claim that no one's "forced" to get an ID. It's just a voluntary thing you do if you want to drive. That may have made sense in the early days of motoring, when relatively few people drove, and most people were rather fearful of cars. Today nearly everyone drives, yet the "voluntary" justification persists. But now we have this little bait-and-switch that says that since ID's are a virtual requirement because it's so difficult to get by without one, there can't be any serious objection to making them mandatory, at least for those who want to exercise their right to vote.
Anyone who refers to the slippery slope "fallacy" (and this isn't directed at you, just at a bunch of Freepers who at various times have insisted that it's just a phantasm) truly is clueless about the way the world works.