It's interesting to see what a curious blend of insightful commentary and completely off-base nonsense Foucault came up with, coming, as he was wont, to the issue without much concern for the actual epistemology of the matter.

The clearest insight is in things like the "myth of factuality" which were indeed very mythical in Foucault's time. The experimental methods were wholly unsuited to very many of the conclusions psychologists wished to draw in the 60s, for instance. I wonder if he came to that conclusion based upon an actual understanding of the methods they used and the questions that they were asking (as a psychology grad student might today), or if he just observed the sociology and inferred that there was no way it could be anything but myth?

The most off-base nonsense is in criticizing psychology for employing methods from other fields. How do you stand on the shoulders of giants but by utilizing previous work? Of course you have to weigh the domain of applicability of the methods, but everyone does, not just psychologists. How ridiculous! We wouldn't have even manged the Industrial Revolution, let alone the iPhone, if we'd taken advice like that to heart.

Psychology lives in a difficult spot because people come with problems that need solving, but our understanding is not at the level of detail to give well-grounded help in all cases. Medicine is much the same; hence "evidence-based medicine" is a thing and not just "Um...yes? How else could you possibly do it?" Nobody talks about evidence-based structural engineering because how else could you possibly do it? But that doesn't mean that it is meant to be a "questioning of the human enigma". It's just a very young science because the system in question is very complicated and our methods struggle with the complexity, and because people want stuff done, it has an especially difficult time keeping opinion and authority at arm's length. Our methods keep getting better, though.