Despite iran’s runaway nuclear program, North Korea’s atomic assistance to Syria, and robust ballistic missile production and testing by Russia and China, a missile defense system for protecting the homeland and U.S. interests overseas remains a controversial idea in some corners. It should not be. The security challenge arising from the proliferation of ballistic missiles and the dangerous payloads they might carry, including weapons of mass destruction (wmd) like nuclear arms, is a threat that — in fact — may be growing.