Well, the problem with psychology is that it challenges a lot of commons beliefs. There's wonderful research that's been done on memory and emotion that people dismiss because they assume psychology is "just common sense", when really, psychology has proven a lot of "common sense" wrong!
And it's no more incomplete than any other science, especially given it's age (only about 100 year olds, as opposed to physics which was being studied all the way back to ancient civilizations). After all, we do not know whether light is particle or a wave, or what causes gravity with anymore or less certainty than we know what causes the mind to work.
Personally, I find the idea of having neuroscience and psychology as distinct fields silly. They are like two sticks leaning together; without one, the other one cannot stand.