Even if we accept that argument, which I think is a little far-fetched given the countries that would need to get on board for a hypothetical food embargo against the US to be effective, there's no national security implications to almonds and there are good substitutes for rice and cotton.
In a real pinch the agricultural production dedicated to ethanol can be redirected to food, and perhaps most importantly even a small shift in the meat/plant balance towards plants creates a huge calorie surplus.
In short, food security looks more like a post hoc rationalization than a good justification for our terrible policy landscape when it comes to agriculture.
American culture can replace it with wheat, yes, but if you ever want a case study on government fiddling with a crop for national security reasons, rice is it. Not in the US, but Asia? It's probably on par with oil.
I think it has more to do with straightforward nationalism. Yes, we could all be sweetening our products with cane sugar and equatorial sugar farmers could be making a great deal of money. But instead we have high tarriffs on sugar cane and subsidies for corn farmers. Why? Because the corn farmers are Americans, and the equatorial farmers are not.
In a real pinch the agricultural production dedicated to ethanol can be redirected to food, and perhaps most importantly even a small shift in the meat/plant balance towards plants creates a huge calorie surplus.
In short, food security looks more like a post hoc rationalization than a good justification for our terrible policy landscape when it comes to agriculture.