I understand your point. However, if most of the steel industry goes overseas and we need to build a military machine in order to fight some war, we may end up with the same problem of treading on eggshells that we have with the countries we buy oil from.
If you go down this road dozens and dozens of industries can credibly claim they are vital to national security. I'd rather risk it in a world where low trade barriers, and the consequent increase and wider distribution of wealth, and the "middle class" values that accompany wealth, makes it less likely we will have to fight wars in the first place. Furthermore there will be multiple sources of steel. What are the odds that Japan/Asia, Eastern Europe, and South America will all simultaneously refuse to service one of the world's largest markets?
Cut the bulldullah. The only real reason for protectionism is protectionism. It raises costs for consumers, lowers competitiveness, encourages monopolies (or dominance of small numbers of large "industry leading" corporations), etc, etc. It does nothing good for anybody except for owners and labor in the protected industries, and it is not good even for them in the long run.