Even great thinkers sometimes speak evil. Plato advocated infanticide because he thought of handicapped children as "inferior creatures." Francis Parkman, one of America's premier historians, associated "Indians" with "leeches" and "contagions." And the 19th-century scientist Louis Agassiz, founder of Harvard's Museum of Natural History, called black people a "degraded and degenerate race." Such rhetoric not only dehumanizes the vulnerable but, as history shows, sets the stage for deadly violence against them.

In late September, Britain's Lord Justice Alan Ward joined the ranks of the dangerously wrong and famous. He decided that physicians in Manchester could separate conjoined twins who shared a common aorta, a surgery that—as expected—resulted in the death of one twin while probably saving the life of the other. In his judgment, Ward said that Mary "has little right to be alive. She … sucks the lifeblood of Jodie and her parasitic living will soon be the cause of Jodie ceasing to live."

As a member of Britain's highest court, Ward has a special responsibility to adjudicate such cases in a way that protects the powerless and the vulnerable. Such prejudiced language, especially by a powerful and respected judge, contributes to the rapid dehumanization of those who don't measure up to contemporary standards of beauty, health, and usefulness. The dangers of such language are documented in William Brennan's excellent (but sadly out of print) book Dehumanizing the Vulnerable: When Word Games Take Lives. Brennan examines the language used to dehumanize oppressed groups throughout history: women, European Jews, blacks, Native Americans, the disabled, and the unwanted unborn.

Oppressors, it seems, are not very creative. In ...