No one with any brains ever pushed corn and corn alone as the solution to our problems. I remember when all this talk was going on there were concerns that we would effect our food supply by pulling only from corn subsidies, and efforts of finding other viable plants were under way (for instance they use sugar cane in central/south america).
Your underlying question seems to ignore the fact that oil isn’t providing all of our energy right now, and its most definitely not dependable (see massively fluctuating prices). There is no one source at the moment that we could rely on for all of our energy, and even if there was we’d be foolish to use only one source in case something happened to that supply.
In the long term though, as oil availability drops off a cliff (which it is in the process of doing), we will have to replace it with other sources… preferably renewable ones. That’s where things like geothermal, biofuels, solar, wind, etc come into play.
Think about this, enough of the suns rays hit our planet in one day right now, that if we converted all of them into electricity… it would only take one hour to power the entire planet for an entire year. Now obviously we’ll never have a 100% conversion rate or 100% of our planet covered in solar panels. But what if we had 1% of our planet covered in panels, and a 50% conversion rate (which is well within our capabilities in the next 50 or so years).