I think we have a disagreement about how to deal with a situation where two different concepts are called by the same name. In some sense they may seem the same because they have the same name, but in another they actually have no relationship. There is no logical path from A to B or vice versa. It’s not like the Norway terrorist was simply disagreeing with cultural Marxism in the academic sense. He wasn’t engaging with it at all, and simply borrowing the term (or more likely, organically reinventing it).
As a simple example, in the conspiracy, cultural Marxism is used nearly synonymously with multiculturalism. Neither of your links mention multiculturalism even once.
Well, coming back to my World Zionist Congress example – you might equally say that antisemites who accuse the WZC of "secretly controlling the world" are not "engaging with it at all, and simply borrowing the term (or more likely, organically reinventing it)". And yet, I don't think that makes sense. Antisemites make all kinds of unhinged, baseless accusations against Jewish people and their community organisations – and yet, that doesn't mean that when an antisemite says "Jew" they are talking about something completely unrelated to what non-antisemites mean by that word – if that were the case, they wouldn't (strictly speaking) be antisemites at all.
And, it is false that "cultural Marxism" the real world academic movement has "no relationship" with Breivik's concept of "cultural Marxism". In his manifesto, Breivik cites figures such as Antonio Gramsci, the Frankfurt School and György Lukács, who were foundational influences on that academic movement. So he is talking about the same thing. That doesn't mean his criticisms of it are sensible, nor do they in any way justify the unspeakable horror of his violence.
Imagine reading an antisemitic screed against the World Zionist Congress, which mentions its real founder and first President Theodor Herzl, and other key early figures such as Max Nordau, Abraham Salz and Samuel Pineles – but then baselessly accuses them of secretly controlling the world's governments. The baseless and irrational accusation doesn't change the identity of the targets of the accusation, it doesn't mean "the screed isn't actually attacking Theodor Herzl et al, rather it is attacking imaginary persons who by coincidence have the same names". In the same way, Breivik's claims about the academic cultural Marxist movement are ignorant and over-the-top, but that doesn't mean he isn't actually talking about them, and instead talking about something completely unrelated.
Language is a tool. We use words because they are useful. As a practical matter, the conspiracy versions of terms have only passing resemblance with their real-world counterparts. Mentioning the relevant people isn’t actually engaging with the content of it, it is more like worldbuilding in a fictional story. New York is a real place but Spider-Man doesn’t live there. MI6 is a real organization but James Bond isn’t on their payroll.
The problem is, where do you draw the line between legitimate criticisms and conspiratorial nonsense?
Again, the Zionist example: there are definitely criticisms of Zionism which are nothing more than baseless antisemitic conspiracy theories (e.g. "Zionist Occupation Government"). But, that doesn't mean all criticisms of it are so baseless. If you read pro-Palestinian authors, or even left-wing Jewish Israelis, you will encounter critiques of Zionism, which whether they ultimately be right or wrong, can't be dismissed on the same grounds.
You will also find claims that some people on the pro-Israel side want to erase the difference between non-antisemitic criticisms of Zionism and antisemitic criticisms of Zionism, in order to put Zionism itself beyond criticism – and I think sometimes those claims are correct. On the other hand, sometimes pro-Palestinian criticisms of Zionism do cross the line into antisemitism, and as applied to those particular cases the claim is false. Part of the problem here, is it isn't always clear where to draw the line between non-antisemitic and antisemitic criticisms of Zionism–it is a question about reasonable people can disagree. Non-antisemitic criticism of Zionism and antisemitic criticism of Zionism aren't totally disjoint, they bleed into each other at the edges.
And I think we have a similar situation with "cultural Marxism". Yes, Breivik's criticisms of it are conspiratorial nonsense – but is everyone else's? There are right-wing criticisms of it which, whether correct or incorrect, arguably aren't "conspiratorial nonsense" – see for an example, see the 2018 article by the conservative lawyer Alexander Zubatov in the Jewish magazine Tablet, "Just Because Anti-Semites Talk About ‘Cultural Marxism’ Doesn’t Mean It Isn’t Real" [0]. There are even left-wing criticisms of it – the cultural Marxist desire to switch the focus of Marxism from economic to cultural issues was (and still is) heavily criticised by orthodox Marxists who view that switch as a distraction and a mistake.
And I see two other parallels to the Zionism case: firstly, just as some Zionists arguably seek to dishonestly erase the distinction between non-antisemitic and antisemitic criticisms of Zionism, in order to put it beyond criticism – in a similar way, my own impression is that some progressives seek to erase the distinction between conspiratorial (even antisemitic) criticisms of cultural Marxism, and non-conspiratorial (even if possibly mistaken) conservative criticisms of it, in order to shut down debate.
And secondly, just as the boundary between non-antisemitic and antisemitic criticisms of Zionism is open to debate, I think the same is true for the boundary between non-conspiratorial and conspiratorial criticisms of cultural Marxism. In my own mind, Zubatov is clearly on the "could well be wrong but not conspiratorial" side of that line, and Breivik is definitely on the "conspiratorial" side of the line – but I'm less clear about where to put something like the Heritage Foundation's criticisms of it. [1] And that's the core problem with your idea that we consider conspiratorial criticisms and non-conspiratorial criticisms of "cultural Marxism" to be talking about two completely unrelated things – it assumes a clearcut boundary between the two which may not actually exist. I think it makes more sense to speak of a continuum of criticisms of the one thing (ranging from the reasonable to the ludicrous, with the boundary between the two being debatable) rather than claiming the reasonable criticisms and the ludicrous criticisms are criticising two completely different things.
As a simple example, in the conspiracy, cultural Marxism is used nearly synonymously with multiculturalism. Neither of your links mention multiculturalism even once.