The 5.9% minimum Ethanol is for the EPA's emissions reduction program. It also reduces Oil consumption so it's a bit of a win win. Needless to say when the original oxygenate mandate was introduced in 90...4? MTBE(a petroleum product) was legal and it was being pushed as the oxygenate until environmental data showed it was leaking into the environment and subsequently banned.
The issue is whether we should allow E15 to be sold like E85 so that people can choose to use it. No one is suggesting we mandate E15 usage. The mandated Ethanol usage is for oxygenate requirements by the EPA. MY 2001+ have been approved for E15 use by the EPA and they're finalizing laws and regulations for it's sale.
What should be mandated or encouraged is FFVs from the manufacturer that can run on Gasoline or Ethanol or a mixture of the two. Right now it's mostly fleet sales and light duty trucks that are FFVs and that means a large portion of new vehicles cannot run E85, (without an aftermarket conversion of some sort).
BTW. Considering the Renewable fuels standard was adopted in 2001, there is no direct correlation between the mandate of Ethanol and your chart. You need a chart of domestic Ethanol consumption to even consider doing that. Another factor you ignored is the cost of Diesel. Please compare all three next time.
