A little exerpt from the website:
The primary reason E-10 ethanol gas is harmful
is because of it's alcohol/ethanol solvent and water-absorbing qualities.
E-10 is also inconvenient because the shelf life of only 2-3 months.
Ethanol (ethyl alcohol) has several chemical properties and effects which render it to be incompatible with engine parts and vehicles -
Alcohols are water soluble, attract and absorb water/moisture, solvent, cleanser and cleaner, drying-agents, de-greaser...and more
Many motors, especially older engines, are constructed with parts that become very brittle over time and cannot withstand the effects of alcohol. When E10 gas is used, the engine components can disintegrate and clog the engine with sludge and grime, causing the engine to "lock up" and seize. When this happens, often the engine cannot be fixed and must be replaced.
Ethanol's effects vary depending on the engine type, model and year and type of fuel system, (Carbureted, direct-injected, 2 stroke or 4 stroke).
Marine engines are probably least compatible with ethanol-blend fuels. Aircraft agencies ban alcohol-blend fuels and are exempt from using E-10 and E-85.
Gasoline absorption of water is problematic (gas becomes contaminated and must be discarded).
Operating an engine on an alcohol content that is too high (over 10% for E10), will cause engine damage and poor performance.