Ethanol is a clean fuel and added as an additive to petrol.
Why can't ethanol itself be used as fuel?
Ethanol clearly can be used as a fuel.
But there are several reasons why it isn't.
First is simple economics. Ethanol costs more to produce than gasoline: oversimplifying only slightly, fermentation is more complicated than simple distillation. Those countries that do use mixtures of ethanol in gasoline do so for "environmental" reasons (which are not always well thought through as being made from plants doesn't make something good if associated production costs are high or alternative uses are better). And "environmental" causes are a good excuse to subsidise favoured groups, like US or Brazilian farmers. In the absence of subsidy, there would be very little use of ethanol as a fuel.
But those are no the only reasons. Ethanol carries less energy than the same volume of gasoline. In other words your mileage will be lower; your fuel efficiency will be lower.
Worse, though, ethanol doesn't have exactly the same characteristics as gasoline. Engines may need to be adjusted so the alternative fuels burn equally well, which is annoying but fixable easily in electronically controlled engines. In addition, Ethanol may be more corrosive to some of the components used in fuel pipes (noting like as bad as methanol, but clearly worse than gasoline). Ethanol is also much more hygroscopic than gasoline, absorbing significant amounts of water from air. This is another potential cause of contamination in fuel systems and may make corrosion worse.
In short, there are no fundamental reasons why ethanol can't be used. But there are a range of practical issues that make it less economical or inconvenient.
Pure ethanol is used as a fuel in South America. Some vehicles can actually produce more power from ethanol than petrol.
It's not used widely mainly because of production cost and energy density that is lower than petrol. for petrol 34.2 MJ/L for ethanol fuel (E100) 20.9 MJ/L.