Not for nothing, If your coastal radars detected incoming, do you know how far they’ll be in flight? They might drop into the sea or maybe onto your cities. JMHO
International law is a little murky in this area. Normally nations announce launches well in advance and take confidence building steps so that no one mistakes a missile test for an attack. The French launch ICBM from the Bay of Biscay into French territorial waters towards the French territory of Saint Pierre and Miquelon south of New Foundland, for instance, probably the closest routine ICBM impacts to the United States.
No one thinks the French are trying to intimidate the U.S. and no one doubts the Norks are trying to intimidate the Japanese.