Thomas Jefferson didn't think that there would ever be shortages of Manufactured goods either. He thought America would just trade for them.
And then in his words "the unthinkable happened". Europe cut us off. Jefferson realized a strong manufacturing base was essential to protecting a free state.
Both Agriculture and manufacturing are necessary to protect a free state. You are only one UN mandate away from a complete cut off of either when you are dependent on foreign nations.
Quite rightly, none of the founders were in favor of federal subsidies to keep any industries going.
But of course we are now net importers of manufactured goods, but still massive exporters of agricultural products.