One of the most shocking openings to any HBO series feels like you’re stepping into a terrifying alternate universe. It’s 1921 in Tulsa, Oklahoma. A white mob that includes Ku Klux Klan members massacres hundreds of Black men, women, and children in the affluent neighborhood of Greenwood. Airplanes drop explosives from overhead. Bullets whiz through the air. Buildings get burned to the ground. The camera follows a young boy trying to escape the carnage with his parents. He’s ultimately smuggled out in a wagon, but his parents die. When I first saw the opening to HBO’s Watchmen limited series, I...