Fuel filters prior to gasahol would completely block water. As to bleach in water passing through with 10% alcohol??? What ever happened to moth balls or sugar in the gas?
This is true in some cases and you are correct that the alcohol would absorb some of the water in the bleach and possibly react to form compounds that wouldn't be good for your fuel system. But most of the water would still end up in the bottom of the gas tank and keep the engine from running.
We have an "STC" (Specialized Type Certificate) to use auto-fuel in our airplane, but we have to test the fuel to make sure that there is no alcohol in the fuel which could damage the airplane's fuel system. To check for alcohol we add water to a test tube with fuel in it and then check the level of the water in the bottom of the test tube. Then you shake it up. If there is alcohol some of the water will be absorbed and the amount of visible water in the tube will go down. If you do not shake the solution the water doesn't get absorbed. It would be the same when you poured bleach in a fuel tank. If you didn't agitate the solution the bleach would tend to just sit at the bottom of the tank and the car would run only briefly and cause little damage. Even if someone did something to agitate the fuel most of the bleach would still end up sitting at the bottom of the tank.
That is why airplanes have a sump in the fuel tanks for moisture to collect in and pilots drain fuel from the sumps into a test tube before flying to check for water in the tanks.
As far as adding sugar or mothballs... any impurities added to your fuel are likely to be bad for your engine. But most of the stories about engines being ruined by people adding things like sugar or mothballs to the fuel are second hand and the damage done is exaggerated. Do you personally know someone who has had an engine permanently destroyed by contaminated fuel? Contaminated engine oil on the other hand can definitely ruin an engine, but that is not what was claimed here. They said that the “inside of their fuel tank smelled like bleach”. This is just silly. Fill a test tube part way with gasohol then squirt a little bleach in it with an eye dropper and do not shake it. Then partially fill a test tube with gasohol. Cover the bottom of the tubes with paper have someone mix them up and see if you can smell which one has bleach in it. Most people's sense of smell will be so overwhelmed by the smell of the gasohol that they will not be able to tell you which tube has the bleach mixed in.
On the hazmat team we had air monitors to sample the air, because your nose can't be trusted shortly after you start breathing most types of fumes.