I don't get why some communists support Iran, it's literally the most reactionary state ever

A lot of “communists” are really just anti-Americans.

They’ll lecture you all about alleged U.S. abuses during the Cold War but suddenly draw a blank when confronted by atrocities committed by the other side. That includes actual professed Communist states like the USSR, China, North Korea, and Cuba, but also theocratic hellholes like Iran who aligned themselves against the West.

In the end, they’ll get behind any state run by lunatics chanting “Death to America” regardless of any other factor.