People don't simply wake up one day and commit genocide. They start by setting themselves apart from others, diminishing the stature of those adhering to dissenting beliefs in small, insidious steps. They begin by saying, 'We're the righteous, and we'll tolerate those others.' And as the toleration diminishes over time, the inevitable harms are overlooked. It is for that reason that James Madison wisely wrote that 'it is proper to take alarm at the first experiment on our liberties'.
