Perhaps I'm confused, but it doesn't look as if you actually gave a few concrete examples of outrages perpetrated by the "New Deal regime". You mention "the Katyn massacre coverup", which I'll willingly agree was a Bad Thing but doesn't seem to me to qualify as an "outrage" (and seems much better explained by wanting Stalin on-side for WW2 than by communist infiltration or approval of such massacres) and "the handling of the civil war in China", on which AIUI the standard view is that the US supported the Nationalists. Reading the OB post to which you linked, and its associated comment thread, leaves me ... unconvinced ... that the standard view is wrong.

McCarthyists [...] did want to make Communism disreputable

Communism was already disreputable. What was distinctive about McCarthy and his allies wasn't that they disapproved of Communism, it was that they claimed there were an enormous number of Communist sympathizers and infiltrators around, and worked hard to get those people into trouble.

Just like today it's by no means necessary to be a card-carrying neo-Nazi to get classified as promoting "hate" by the SPLC.

This seems like a strange analogy here. The SPLC, so far as I know, isn't claiming that the people and organizations it criticizes are neo-Nazis or neo-Nazi sympathizers. It's claiming that various entitles are "hate groups", and there are varieties of hate other than Nazism. (I make no comment on how much of the time they are right; I just don't see that there's a good analogy between McCarthy saying "X is a Communist" when X isn't a Communist, and the SPLC saying "Y is a hate group" when Y isn't neo-Nazi. Because Communist = Communist, but hate group != neo-Nazi.

the McCarthyists were by no means the first ones

For me, whether an action is good or bad, or sensible or foolish, has scarcely anything to do with whether other people have done similar things before. Do you take a different view?

By the way, did you know that the media assault on [McCarthy] was in fact CIA-orchestrated?

The link you give doesn't make or support that claim. It does say (with an absolute absence of specificity about what they did) that the CIA attacked McCarthy, which is not the same thing. And the source it cites doesn't seem super-credible, though perhaps you know more about its reliability than I do. (Incidentally, since you seem to think "But he started it!" a fair rejoinder in cases like this, I remark that according to the page you linked to the CIA's attack on McCarthy was precipitated by McCarthy's attack on the CIA.)

it shows a huge lack of perspective if you believe that McCarthyism was somehow novel or unique in pushing the idea that people's careers, especially public careers, should suffer if they commit certain ideological transgressions.

No, I don't think that. I think that that idea was one of the distinctive features of McCarthyism. (Similarly: Christianity's belief that a god exists is neither novel nor unique, but a purported summary of what Christianity is about that doesn't mention that belief would be insane.)

ever since the New Deal

Er. Are you suggesting that the idea of punishing people for ideological transgressions -- which we agree was by no means invented by McCarthy -- was in fact invented by the architects of "the New Deal"? Or that FDR's administration was particularly given to doing this? If so, I would be very interested to see your evidence. -- Perhaps you're merely saying that McCarthy's anti-Communist activities were the rough equivalent of some anti-something-else activities engaged in by the FDR administration; if so, then again I would like some details.