“Water down the fuel” is pretty close to true and, at a minimum, more true than false. The energy per gallon of ethanol is around 2/3 that of gasoline, so the more ethanol you mix into a gallon of auto fuel sold at retail, the more “watered down” that fuel is.

Ethanol is also hygroscopic and the resulting blended fuel is nowhere near as shelf/tank stable as a pure gasoline fuel, resulting in more service/repairs. (I have to change/clean carbs on my lawn mower/snow blower at least every other season if I leave any ethanol mixed fuel in it. That sometimes, but much more rarely, happens with pure gasoline, even E0 regular auto fuel.)

You're more than welcome to disprove any of it using facts and citations.

Edit: since my original comment was censored, I'll add context here - it was suggesting increased gasoline engine degradation resulting from altered fuel mixtures.

Citations?