How do you mean mixing fuels being silly? I’m no expert but it seems quite common - hybrid vehicles for example; biodiesel with petrol diesel (and other things like motor oil); and not sure about gasoline but it seems to commonly be mixed with other things like ethanol.
Silly in that it is not necessary. Any ICE vehicle can be converted inexpensively to burn pure ethanol, no petrol required. Any diesel will accept biodiesel as fuel without mixing with petrol. If fossil fuels are a problem, and ethanol and biodiesel covers all petrol applications, why bother keeping petrol around?
