Those who are comfortable with allowing California to do this should ask themselves whether they would likewise embrace state action from afar if it imposed costs on them. For instance, how might they feel if a consortium of "red" states adopted school textbook standards that required the teaching of intelligent design alongside biological evolution—and those red-state textbook regulations influenced what the children in "Blue" states were forced to read? Or if a group of states in the thrall of anti-childhood-vaccine activists adopted regulations that effectively removed crucial vaccines from other state markets?

States have the right to act. But their reach should end where another state's nose begins.