Who ever who told you that is full of sh1t, There are many side effects that ethanol can cause but that is not one.
Ethanol can eat up old rubber fuel lines (pre 93), weaken some older cheap metal tanks etc. and also damage some older injectors as well. All of today's engines and fuel systems are 100% ethanol compatible
Ethanol will not seperate from gas, It will collect moisture in an unsealed fuel system though.
There are too many myths and truths to but in one thread but the guy who told you this is totally uneducated on methanol.