They don't have to actually launch their weapons to change our policy. I'll reference again Gen. Xiong Guankai's thinly veiled threat to nuke Los Angeles if we came to Taiwan's defense. Our calculations of what's an acceptable level of friendly civilian casualties isn't shared by all of our possible opponents. L'il Kim's already starving a very sizable fraction of his population, and none of his generals are terribly interested in telling him what he doesn't want to hear. What's to say the pompadored psychopath won't try lobbing a Taep'o-Dong-1 at Hawaii? You really want our only option in that case to be mourning the population of Honolulu and then vaporizing everything between the 38th parallel & the Yalu River?
This isn't paranoia, it's contengency planning. Between WWI & II we had an assortment of naval war plans listed by color codes. WP Black was Germany, Orange was Japan, White was a domestic uprising (parts of which were activated in response to the Bonus Army protests of 1932), Grey - a carribean nation, Green - Mexico, Purple -a Latin American country, Gold was France (They were taken quite seriously until 1939...), and Red was our special allies in the UK. Gold & Red were considered very unlikely, but they were prepared for nonetheless. When the feces impact the ventilator, it's too late to start drawing up plans from scratch. Likewise, when the missiles are in flight, it's too late to start building lasers & ABMs.