Given the unlikeliness of ever being at war with every significant steel-making nation in the world at the same time (assuming for the moment that, unprotected, we wouldn't have any significant domestic capacity for steel production), no, I don't see how relying on foreign nations for steel is insane, especially since to get to that point, the foreign nations would have to be doing a better job of delivering steel than the domestic steel industry. It strikes me as more insane to wed yourself to an inferior product (be it in price, quality or whatever area makes the foreign supplier better) in order to maintain some self-sufficiency in something you'll likely always be able to trade for.