We need to define flight here: "a brilliant, imaginative, or unrestrained exercise or display" [1]. So he fulfills himself as a a brilliant, imaginative, or unrestrained exercise or display. He toots his own horn, to promote oneself; to boast or brag; to tout oneself [2].
What does the quote mean?
They (some doctors and professors in this quote) have abdicated their freedom to their discipline or interest. They see all things through the single lens of their discipline, and all things outside of it as trite, "stupid", something not to think on at all or to think of only in how it relates to their specialty.
Take the result of Zuckerberg's "need" to monetizing Facebook. This has dire consequences on peoples security, and even peoples personal sanity. To Zuckerberg these things are dealt with in a way "lacking in sensitivity, intelligence, and humanity", all that matters is Facebook's bottom line. Further on in Simone de Beauvoir's Ethics of Ambiguity she quotes "The rest of the world is a faceless desert. Here again one sees how such a choice is immediately confirmed. If there is being only, for example, in the form of the Army, how could the military man wish for anything else than to multiply barracks and maneuvers?"
The overall idea being that people highly specialized and competent in one area make the logical fallacy of arguing from authority (themselves being the authority they are arguing from) and put forth the most mundane, lacking in nuance "ordinary values" in areas that they have little understanding, haven't researched and aren't really interested in.
1. https://www.merriam-webster.com/dictionary/flight definition 5