I understand the skepticism from both sides. I, too, like to see the proof.
I read somewhere something to the effect that too many people put too much emotional energy into disliking it.
off the top of my head, I recall that...
ethanol, while higher in octane, has a much lower specific output- hence the lower mpg
also ethanol is much more hygroscopic than fuel. absorbing water can cause corrosion over time.
ethanol is also not as good a lubricant and is tough on valves and valve seats
ethanol falsely increases the O2 sensor readings making the engine run leaner leading to drivability problems.
Here's an article outlining an experiment of ethanol blends and engine durability.
Do I think ethanol problems are blown out of proportion? Probably yes.
Would I run non ethanol gas if I had the choice? Most likely yes (depending on the price)
All that said, I am not an engineer nor a mechanic.
And this thread wasn't started about ethanol.