Science that dabbles in the metaphysical and the untestable is inherently soft. It sticks more as a language or idiom that quickly or easily describes something, rather than a satisfactory explanation.
e.g. psychoanalysis. It's almost thoroughly discredited by now, yet persists. It lingers as a shorthand that can express facets of our existence. Everything from "Freudian slips" to "Oedipal complexes" and "Ego/Id" to the cryptic nature of dreams. It's convenient, and therefore works on some level. I would suggest it functions on the same level as the Middle Ages concept of the bodily humors. It's total bunk, but a colorful descriptor.
It's myth at its truest. A descriptor that is less concerned with truth (though it may indeed be true) than it is with being archetypally pleasing.
Perhaps this is increasingly true of nature/nurture and even evolutionary descriptors. Maybe there's a lot there. Maybe it's just very colorful.
