Earlier quoted context omitted.
>the Soviet Union was arguably fascist // You appear to be starting from an assumption that everything USSR did, politically, was left-wing; and thus concluding that fascism can be left wing. A dictator is diametrical opposed to left-wing ideology. What you're doing is like saying uxoricide (murdering your wife) is part of FOSS, because a proponent of FOSS did it.
> You appear to be starting from an assumption that everything USSR did, politically, was left-wing; and thus concluding that fascism can be left wing. No, I did not. Basically I'm arguing that the USSR pretended to be "left-wing" but were actually "right-wing". So perhaps they were fascist, but that doesn't imply that truly left-wing governments and movements are fascist.
It's the natural progression.