You should lose 3% MPG MAXIMUM with E10. At 15MPG that's less than 1/2 a MPG. Any loss that large means something is wrong.
We have an excess of arable land so the food vs fuel argument is not really relevant here just yet, not even close really. In the future we will need more sources of Ethanol besides Corn but we're already exporting over a billion gallons for lack of Domestic demand.
That's almost 1/10th of our current production! But what are they going to do? Punish the Ethanol plants for doing their job?