I doubt that many people still hold this uniquely American view, since Communism has collapsed and the social features in question still thrive without any assistance from agents of foreign powers. When one used to point out to the folks who made this argument that all these were strongly suppressed in most Communist countries and denounced as forms of Capitalist corruption by them, they would reply that of course the Communists wanted to keep such filth out of their own lands–the goal was to weaken ours.
This argument is almost too silly to answer, but it worth noting that in the very earliest stages of the Russian revolution there was indeed a good deal of experimental art and music as well as sexual experimentation. Stalin, however, was far more bourgeois than revolutionary in his artistic tastes and morals, and suppressed such modernism as severely as did Hitler on the extreme right.
There were isolated exceptions to this pattern (art and music in Poland, fiction in Cuba, for instance), but generally where Communism prevailed there was a stultifying imposition of conservative artistic standards.
Those who used to make this argument probably knew little or nothing about this history; they simply associated Communism with everything they disliked. By the 1950s it was already a joke that conservatives would call anything new a “Communist plot.”
Of course, many experimental artists in Western countries became involved briefly or for longer periods with Communist movements, but in most cases they were drawn to them because their rebellious artistic tastes naturally led them to sympathize with revolution itself rather than their politics having caused their works to become more experimental.