Biofuels burn less carbon than petroleum and should be included in any balanced way to lower carbon emissions. Corn ethanol gives farmers incentives to grow more corn for ethanol and less for feeding livestock. The trick is to get farming equipment and transport trucks to burn less gasoline, otherwise it costs more carbon to farm the corn than it does to make the corn into ethanol to reduce carbon emissions later.
No, corn ethanol should not be emphasized in the fight against global warming, because global warming is not so critical that corn ethanol needs to be involved. There are other ways to combat global warming, for example by iron algae blooms, so corn ethanol really does not need to be a player in the fight on global warming at this point.