[Fears about 4th Amendment encroachments, privacy, and infringements on individual liberty] are not, as the Court would have it, solely the lot of the guilty. To be law abiding is not necessarily to be spotless, and even the most virtuous can be unlucky. Unwanted attention from the police need not be less discomforting simply because one’s secrets are not the stuff of criminal prosecutions.
Moreover, those who have found - by reason of prejudice or misfortune - that encounters with the police may become adversarial or unpleasant without good cause will have grounds for worrying at any stop designed to elicit signs of suspicious behavior. Being stopped by the police is distressing even when it should not be terrifying, and what begins mildly may by happenstance turn severe.