Video recently emerged of a black man behaving erratically and threateningly on a crowded New York City subway. When he seated himself next to two women, they got up and moved away, but the man forcibly grabbed one of them and sat her back down. The woman, with eyes closed and terror on her face, repeatedly mouthed, “Help me.” Nobody flinched. They watched (and filmed) as this man, probably no more than 150 pounds, then shouted at her, grabbed her by the hair and shoved her. “What does it say about society that not a single man stepped in to...