The Risks of Taking Up Shields

In the nuclear age, it may be safer when each side has only spears

To President Reagan, a foolproof system for shooting down nuclear weapons is nothing less than "a new hope for our children in the 21st century." Such an antiballistic missile (ABM) umbrella, he said, would make the U.S. safe from attack, the world free from the danger of cataclysmic conflict between the superpowers, and the doctrine of deterrence more credible—and far more humane—than the traditional reliance on the threat of massive retaliation.

To many experts, however, Reagan's dream of a "truly lasting...