Recording events from public land shouldn't be a crime. Yet when a woman in Utah, standing by a public road, filmed farmworkers pushing a cow with a bulldozer, the farmer drove up to her and said, "You cannot videotape my property." Soon the police came and local prosecutors charged her with "agricultural operation interference." They dropped the charges several months later since she was on public land. But what if she'd posed as a farmworker, got a job on the farm and then secretly recorded what she saw? Increasingly, activists do that. More than a hundred such undercover investigations have...