The fake explanation. What does the claim of 'civilization' and 'decency' add to the assertion?

I added these word specifically to parallel the paraphrase of Malcolm's claim. The rationale for their use is that there exists a specific (if somewhat vague and, on some dimensions, disputed) cluster in the space of all possible systems of social norms that is commonly associated with these words in modern English. Among other things, this includes a negative attitude towards public judicial torture and open repression of (some kinds of) anti-government speech (relevant for my example), as well as towards assassination plots against foreign leaders (relevant for Malcolm's example -- and possibly a matter of greater outrage back in his day).

So it's not a fake explanation, because it points to a real existing cluster of norms that have been dominant in the Western world in recent history. This can in turn be used, for example, to point to other norms in this cluster and predict that they are correlated with the listed examples across societies.

Note that here I'm merely using these words with their customary meaning, not to express unreserved approval of this entire cluster of norms.

It also seems like (when you speak of "probability") you're defending a statement that Perloff does not record Malcolm making, while criticizing Wittgenstein for traits this particular passage does not clearly show.

As I already pointed out, we are not judging Malcolm and Wittgenstein as two equal participants in a debate. Rather, we are discussing whether the latter's criticism really is up to such high standards that it deserves being extolled as a sterling example of rational thinking. Hence my sticter scrutiny of him, and my tendency to give maximally charitable interpretation to Malcolm.