Some American socialists and anarchists opposed the communists.
I think Sydney Hook, for example, remained a socialist. He spent a big chunk of his life fighting communism in the U.S. and abroad.
I suspect that those are few and would ask, at least in today's terms, what's the difference? I realize there was a time when the ideologies were unique from each other, but I believe that today they are all driven by essentially the same goals, the destruction of capitalism and the insertion of an authoritarian, centralized, nanny state government.
There may even be a majority in their ranks who don't see that as the goal, but in the end I believe that is what they are fighting for regardless of their intent.
The communists had a plan and we see continue to see it in process today.