It is in line with the categories of the accusations made in that time. This is effectively a loyalty accusation: by seeking to mediate, he has shown himself to be insufficiently committed to the cause of racial and gender justice, which consequently means his motive must have been to defend the racist.

Yeah, but "making loyalty accusations" isn't exactly what Stalin is known for. He's known for a brutal purge that sent his political enemies to death camps.

To Godwinize for clarity: this is like using "Hitlerian" to celebrate a public policy achievement in passenger rail scheduling.

It is at the core of the worldview and ideology he espoused. The actions he is known for flow out from that ideology.

In this case I suppose "Stalinist" is a metonym for the apparatchiks who enforced ideological purity in institutions and made sure that deviants got punished.

Maybe it'd be more accurate to call it McCarthyist.