Would our hypothetical history-reviewing rationalist, then, also conclude that communist infiltration -- even on the grand scale you say it achieved in McCarthy's time -- was not such a bad thing?
It's hard to weigh these kinds of alternative histories. Given their strategy of supporting protest movements, and indeed, getting in front of every parade they could, I'm sure they lended impetus to a number of good movements. On the other hand, when they got out in front of the movements, they would alter the course of the movements. Whether the net perturbation was good depends on your values, and the empirical facts of how large and in what direction those perturbations were.
Me, I'm not very fond of communism, so I find the lingering effects of their ideology harmful.
On the other hand, when they got out in front of the movements, they would alter the course of the movements.
Alter to what? You are implying some sort of underhanded maneuvering that I not sure ever actually occurred.
After Civil Rights, Martin Luther King Jr was moving to topics of that are still controversial today - like ending the Vietnam War and ending pervasive poverty. As you say, one's the net effect of that change depends on one's prior values. More importantly, I think these types of change were organic to the movement that King was leading, not imposed from above.
I have found this most wonderful (if fairly lengthy) article, and thought you would enjoy having it brought to your attention.
It is so good, I think we should include it among the references in the "Politics is the Mind Killer" wiki page. But, before that, I submit it to you, and ask you: is there anything in this article that would warrant its exclusion from this site? I mean, besides the fact that it is about politics, and written by a notorious Social-democrat (And is that in itself grounds for exclusion?).