Two funny things: 1) originally environmentalists thought they could make common cause with midwest corn farmers by backing ethanol as a green fuel; that was back in the 80s; 2) for decades now environmentalists having been arguing that we should remove ethanol subsidies because they don't work as promised and have enormous negative externalities of their own. And regardless of the positions of the environmentalists they remain the boogeymen of the right and thus midwestern farmers. Now they, not the farmers, are the ones responsible for the fertilizer runoff and algal blooms. It's almost as if the actual positions of environmentalists were never the issue for those who hate them.
Another funny thing: in your view of the world the entities that made money off this situation -- the farmers and agribusiness -- and the entities that have continuously fought for the ethanol subsidies since they were introduced bear no blame for their negative consequences. The environmentalists, who were their allies initially and have fought them ineffectually now for decades, are entirely responsible. The environmentalists are simultaneously the only people with agency and responsibility in this scenario and largely ineffectual while the farmers and agribusiness are just a force of nature. They bear no more responsibility for their actions than lightning does when it strikes a tree. They are powerful, dominating even, but blameless.