Food security is the reason governments stick their noses in an otherwise free market.
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.
Not that I don't think the sugar subsidies specifically are nonsense, the structural reasons that food subsidies exist is sound.
http://ourworld.unu.edu/en/can-we-feed-our-world-without-mon...
They do spend millions of dollars lobbying the government every year.
https://www.opensecrets.org/lobby/clientsum.php?id=D00000005...
Soy seems to be in a similar situation to corn.