Ethanol is wildy bad for the environment and is raising the cost of food.
I read somewhere awhile back that it takes something like 3 gallons of gasoline (through running farm equipment and transportation) to make 4 gallons of ethanol. That coupled with ethanol being less efficient that gasoline and causes more wear and rear on vehicles probably means that if we ditched it altogether we'd probably the same carbon emissions wise.
Also, for every acre of corn raised to go into ethanol, that's one acre not going into feed corn or other food crops so we're effectively raising the cost of food via limiting supply and competition.
The only people that benefit are farmers that recieve substantial subsidies to grow it and government personnel who administer said subsidies and elected officials that campaign on taking money from you the tax payer and funneling it into these programs.
The cost to all of us is diffused, probably no more than a few tens of dollars taken from us via taxes so nobody is gonna go stand up to these people and demand that we end this subsidy. The benefit to them is very focused and large so they have every interest to keep the cash flowing their way. Every interest to take money from all classes of people but most damaging to the poorest of people since those dollars mean more to them than richer peoples.
This wildest part is that you who is reading this right now is probably outraged that this program is in place but the even crazier part is that you can substitute this with practically any and all industries and they are all doing the exact same thing but for the things that you agree with, are perfectly fine with keeping those subsidies flowing. After all, it's only the other people that are greedy. The only real solution is to completely end all federal subsidies but I'm sure you'll disagree and say that XYZ is necessary because it's your special interest.