It's bad enough we have to deal with 10% ethanol content in our gasoline all in the name of clean air and less dependence upon foreign oil sources. Considering that ethanol provides neither makes it even more of a pain. All ethanol does is eat up tax dollars (it's heavily subsidized), provides nothing in the way of reduced carbon footprint (we use just as much petroleum growing the crops and processing them into alcohol as we would if we did nothing), and increases food prices because farmland that in the past has been used for food crops are now being used to grow corn as feedstock for ethanol production. Ethanol in gasoline also decreases fuel economy (ethanol has ~50% of the energy of an equivalent volume of gasoline).
There's also one more bad side effect of ethanol many of us who are boaters have to deal with on a constant basis – fuel separation. When water gets into the gasoline/ethanol mixture the ethanol separates out of the gas and creates a sludge that clogs fuel filters and fuel injectors. In a marine environment it is inevitable that water will get into fuel tanks, mostly through condensation, because marine environments are humid.
Now the EPA wants to add insult to injury by increasing the ethanol content from 10% to 15%. That means more tax subsidies to ethanol producers (meaning more of your money coming out of your wallet to pay for it), more pressure on food prices as more farmland is used to grow corn for ethanol production, and even poorer fuel economy for you vehicle (which means even more of your money coming out of your wallet to pay for it), with little to show for it in regards to air pollution, carbon footprint, or reduction in dependence upon foreign oil sources.
If ethanol was such a great deal there would be no need to subsidize it. And with a higher alcohol content the fuel separation problems will get even worse. The existing problem seen in boats costs the consumer millions in repairs and remediation. It will only get worse if the ethanol content is increased.
By the way, have you noticed the EPA doesn't mandate use of ethanol in aviation gasoline? That's because they know there would be lawsuits up the wazoo as the number of plane crashes (and fatalities) would skyrocket due to fuel starvation caused by the ethanol separating out of the gas and clogging the fuel systems. (This refers of course to piston-engined aircraft.)