It’s just weird because it seems like libertarianism should be the opposite of fascism. But I’m probably overthinking it.

Libertarianism is just Republicans but without the theocratic fetishes.

The opposite of libertarianism is a democracy that protects citizens’ rights against the state (civil liberties) and minority groups’ rights against the majority (civil rights). Face value libertarianism protects civil liberties but not civil rights. Fascism protects neither.