This is also a lie purpetuated by commies. That Stalin killed all those people because he was just a dictator, not because he was a communist. While debatable, I believe the bloodiest and cruel things he did where in the name of communism.
Oh, I definitely disagree with it.
That's why Stalin gets some casual sympathy in pro-authoritarian right wing circles, because he is definitely seen as another of harsh Russian authocrats and his rule and his purges were made in vast majority to destroy any possible rivals in party and military (which later crippled military in WW2). I don't think in his dictator stage he cared about much else. And politics towards both economic and social issues was very fluid and without much regard for communist orthodoxy.
Just like modern China PR's aparatchiks are still venerating Mao as new Yellow Emperor, but they are in general way much more inheritors of old Chinese buerocracy.
It's an interesting thing trying to figure out how many people were killed by communism. Then you come to the realization that it'd be a lot less if the USG had gone after the commies in our own government that McCarthy warned about. Communists in the Dept of State slow-rolled aid to Chiang Kai -Shek, forcing a retreat to Taiwan and letting Mao take over. No Mao = no Korean War and no Vietnam War...
In terms of stopping Asian revolutions yes. Then of course Asian revolutions even more than Russian reversed to very traditional Asian modes of government quite quickly.
The dynamics of Russian or Chinese societies are really powerful and well rooted. Whoever takes power - he'll most likely be assimilated (I mean Chinese assimilated Mongols and Manchu, no wonder they assimilated own commies
)
Of course that makes them ultimately much more dangerous politically for USA than actual commies. Ironically.
Other supposed security risks were figures like Gustavo Durán, who was a Spaniard who had fought against fascist Franco before fleeing the country. Franco basically declared everyone who fought him as communist.
While anti-Franco forces were more than communists - various forms of communists and socialists were definitely dominant players, overshadowing centrits, and even more majority among migrants (because they were harsher persecutions among them). Duran himself was socialist.
Now of course not every socialist was Soviet agent in fact Stalin-aligned communists in certain period waged internal persecution among Republican forces against anarchists and anti-Soviet less radical socialists (which as one could guess did not help Republican cause at all).