The International Communist League, represented in (english) Canada as the Spartacist League, have a theory of anarchism emerging specifically as a result of the "low tide" or "movement interregnum" that followed the last cycle of struggle. In other words, in pissing-contest fashion, the line is put forth that because the left is weak, well-intentioned people are drawn towards anarchism. (In so doing, they seem to draw on Lenin's accusation that "Anarchism was not infrequently a kind of penalty for the opportunist sins of the working-class movement.")
The emergence of anarchism as a prevalent ideology among radicalized youth today is a reflection of what we Marxists understand as a global retrogression in political consciousness following the fall of the Soviet Union in 1991-92 and the restoration of capitalism in the Soviet degenerated workers state and the deformed workers states of East Europe.
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The implication being that a strong and vibrant left would see the decline of anarchist ideology.
Now i'm not an anarchist, nor am i a Trotskyist, so in the pissing-contest sense of this discussion i can say "i don't have a dog in that fight." But as a member of the radical left, as a post-anarchist leftist, i am interested in what evidence supports or contradicts this theory.