If a particle physicist discovers something basic in his own specialty, it affects all of physics -- for example, the mass of neutrinos or the presence or absence of a Higgs boson. Cosmologists must pay attention to particle physics, even though particle physics and cosmology would seem to be spectacularly dissimilar.
Such a scientific theory is a two-way street. If cosmology comes up with something like dark matter or dark energy, based on solid observation but not explained, this affects particle physics, and work begins immediately to explain what has only been described. The reason is that the central scientific theory, that defines physics, also unites it.
Psychology doesn't have such a theory -- there is no overarching theory that unites the 53 subfields recognized by the APA, which consequently operate independently of each other and of any serious concern about theoretical implications.
So when you say that there is real science taking place in some of psychology's subfields, you're absolutely right. But if someone wants to imply that this means psychology is a science in the same way that physics or biology are sciences, they're absolutely wrong.
> to dismiss all of psychological science as illegitimate is to ignore a tremendous amount of progress in understanding and human well-being that has come in the past century.
When Michelson and Morley falsified the ether theory in 1887, every living physicist knew exactly what that result meant -- it pulled the rug from under electromagnetic theory and left it unexplained. No one tried to say, "but those other physicists are still doing good work." That's not how science works.
I will know psychology as a field has reached the threshold of science when psychologists courageously propose a central, unifying, falsifiable theory, amenable to practical test that, if it fails, invalidates the entire field. And I won't hold my breath for that development.
Physics has such a theory. Biology has such a theory. Geology has one. Any of those theories can be tested -- indeed, is regularly tested --and the failure to falsify those theories is the only reason for the standing of those fields as sciences.
Science is not scientists working in isolation, in a theoretical vacuum, on studies that cannot be replicated, as with psychology. Science is instead the building of a defining theoretical structure, constructed on a scaffolding of evidence.
> and human well-being that has come in the past century.
That claim is completely falsified by the recovered memory therapy debacle of the 1990s, which singlehandedly erased any public goodwill toward the field of psychology and sowed an atmosphere of distrust that will require many years to dissipate. And recovered memory therapy is just one of many examples in recent times that reveal the danger of not shaping a guiding theory that simultaneously informs research and controls the behavior of clinicians.