My auto-fuel-stc says very clearly that one cannot use gasoline with
any type of alcohol in it. I understand that beyond the reg itself, the
main reason is that fuel lines can swell if they come into contact with
alcohol cutting of the flow of fuel to the engine.

I'm going to obey the reg (really. actually, honestly.). I'm just curious.
How likely is alcohol to actually hurt or stop my engine or airplane?

-Just Curious
-A Cessna 150 Driver