> Isn't iterative improvement what all science is about?
Yes and no. There's more to science, but iterative improvement is a large part of it.
My issue with psychology (and other soft sciences, e.g. sociology, economics) isn't so much its striving to find answers, but its adopting a one-sided worldview before that striving, thereby coloring their findings with that one side.
Look at what you wrote--'I know it [psychology] is typically viewed as a 'liberal' field'. That's because it IS a liberal (well, a politically Progressive) field--its instructors, its researchers, its practitioners largely are self-admittedly liberal (and further Left on the political spectrum.) And when they hire, they hire like-minds.[1] (Which is a thing humans do--no one wants to work with people they... dislike... for some reason.)
And so, because they've no opposing worldview in their ranks to say 'no', well... can their findings be trusted? [2]
[1] A commentary on the perceived political homogeneity at the University--https://scholar.princeton.edu/sites/default/files/the_value_...