But it purely postmodern fashion (*wink*), I think we should see it the other way around: we write laws to restrain ourselves, not the evil-doers. (I love that term, I really think we should use it more often. It's catchy.) There's a reference attached below, which reads (for the sake of context)
Probably all laws are useless; for good men do not want laws at all, and bad men are made no better by them. (Demonax)
Perhaps we shouldn't think laws useless, but rather consider what would happen without them: without laws, how would you react to a grievance? Would you carefully apply eye-for-an-eye repayment? Would you consider death an appropriate punishment for any harm done to you or those you love? Would you feel it necessary to make it plainly obvious to all evil-doers just how painful such activities could be? Without laws holding you back, how far would you go?
Criminals do not feel the restraint of law: other than perhaps some cost/benefit analysis in view of potential punishment, the law is just a text, written by others to protect them. With the power to disregard those laws, they no longer matter. But they do matter to those who write them and abide by them: writing them and ignoring them would be ... an exercise left for the reader.
Laws don't keep you safe from your neighbor, should he decide to carve you up with a chainsaw -- they keep him safe, should you decide you don't appreciate it, assuming you obey the law. Should you decide to "take the law in your own hands," the law protects you from excessive reprisals for your lawless (but righteous?) retribution. Laws truly are written only for those who will obey them, and it seems all reversed and wrong, but isn't that the only way it could be?
Anarchy is often portrayed as a bunch of people doing as they please, usually in the style of Mad Max -- lots of shotguns, dirt bikes, and blood. The big difference between that world and ours is self-restraint, expressed as laws: promises to those who don't obey them that you, though powerful and righteous and angry, set limits for yourself in your revenge. For those interested in setting humans apart from animals (or "other animals," depending on your worldview) this is another opportunity to do so.