Why might democratic nations be fearful of authoritarian or fascist leader

Mostly so the people can still have power.

Explanation:

Authoritarian and Fascist leaders are usually dictators, with absolute power, denying people's human rights to create stability in their nations. A democratic nation with good human standards would have people who'd like to keep their rights. Only in vulnerable or unstable nations can real takeovers occur (sometimes, stable nations have problems).

then its a law the end