Earlier quoted context omitted.
I'd guess the Polish rant is based on that Soviet really did support the anti-nuclear weapon movement, and so on. Seing conspiracy theories like those, I am strengthened in the belief that the US extreme left and right are equally crazy. In Europe we mostly see the Chomsky brigade, some variation would make it less irritating.
That rant also ignores the fact that after the 1930s (and particularly after the Spanish Civil War) it was clear that the Soviets regarded any "socialists" who weren't under their direct control as more of a threat than their apparent enemies. Most socialists in Western Europe (e.g. the UK Labour Party) were more afraid of the Soviets than those on the political right.
(There were also anarchists etc, but in general the non-communist extreme left-wingers were few before ~1968, when they got more numerous and varied).
Also, I remember reading surprise after 1989 on how much control Soviet had over the West European communist parties. E.g. that the Italian communist party had such an accomodating attitude by order (Soviet wanted to get a de facto split in Western/Eastern Europe.)