Opposite likes north and south are opposites? Or opposites like apples and oranges are opposites.

Fascism and communism are both:

• authoritarian attempts
• to improve socieity
• by radically changing economic relations
• from consensual trade to slavery
• to support a massive war effort
• designed to get the rest of the world under the same authoritarian regime
• resulting in millions of battlefield deaths
• and the deaths of millions of enslaved citizens
• by overwork, disease, starvation
• and outright systematic execution

But one’s “left wing” and the other is “right wing” so they could be described as “opposites”.