It is to make your project seem less dogmatic, and yourself more humble.

Here,

> Anthropologists are not qualified to decide whose job is bullshit and neither is anyone else

This is performatively false: he wrote a book on it.

The economist's rebuttal was to claim that making a meaningful contribution to the world was, in the opinion of the author, "a high bar to clear" for job doers and try to supplant that only with "I have the feeling of being useful" as sufficient for a job to be not bullshit.

It's not trying to undermine the concept of defining jobs by what the job doers say about them.

Thus by simply redefining "non-bullshit jobs" as jobs which are useful to someone rather than useful to society at large, the economist makes no actual comment on the "zero sum jobs" component of "bullshit jobs".

This is such bizarre reasoning it stunned me. The point of the book as to describe a trend of people feeling that their jobs were pointless, "Bullshit", so to speak. But going from there to assuming that the book asserts a universal criteria for what job is Bullshit, without even reading the book, is ???

> Anthropologists are not qualified to... Anthropologists however are trained to... ... a bullshit job is defined as ...

I am not qualified to do X. However I am qualified to do Y. Ah! Y enables me to do X. So let me do X.

The first sentence there is a lie to massage the impact of the later ones. He literally defined what a "Bullshit Job" is, he wrote a book about it. The conceptual scheme of the entire book is his. He wrote the surveys; he defined the topic.

The idea that he is just a passive receiver of a coherent theory of jobs is false; and this is just a rhetorical gambit to disguise the fact that, no, he is the major architect of this idea and of the whole project.

And this becomes more blindingly obvious when other people attempt to repeat a survey asking whether their job is "bullshit" and find only 5% of people saying so.