Hi Harry:
Holy smokes,......where do I begin???
1) Ethanol is corrosive. It attacks all the elastomers in the fuel system and anything not Viton isn't long for this world.
2) Ethanol is hygroscopic as the dickens. Any and all moisture is absorbed and then attacks ferrous parts in the fuel system. In the case of CIS, the stainless steel parts in the fuel distributor suffer accordingly. Water-based corrosion is a problem for any carbureted or MFI system and requires diligence in maintenance procedures.
3) Ethanol has far less BTU's/gallon than gasolines as well as other alcohols. Even Butanol would have been a better choice. This sometimes requires mixture changes and fuel economy and performance both suffer. There are political arguments to be made about the need for 1/3 more fuel to travel the same distance.
4) Ethanol is not miscable. It tends to separate out of gasoline and thats not a good thing at all.
Now, Ethanol has a high octane rating so its good in some circumstances such as EFI'ed Turbo engines that require high-octane fuels to survive and one has full control over the fuel mixtures.
JMHO, but this E10, E15, and E85 situation will be an unintended windfall for the auto repair industry as people struggle with the effects of these fuels in cars that were not made for it. Politics Trumps Science,...(again).