If they launch a sneak attack like that, why shouldn’t we just respond by emptying our silos and SSBNs at them?
Because as soon as they see our missile launches, they will launch at our cities?
Let's say Iran is secretly supplied with new Chinese or Russian long-range anti-ship missiles. We go into the Persian Gulf with a Carrier Battle Group, with another two CBGs in the Indian Ocean on standby. The Iranians launch a swarm of missiles that sink all three carriers, and most of their support ships, wiping out over a quarter of our carrier assets.
Now, are you going to nuke Tehran and Qom in response, killing millions?