Sorry, your question is fair -- let me elaborate: I feel the OP puts forward two statements, categorizing depression as "adaptive", or "adaptive response taken

Sorry, your question is fair -- let me elaborate: I feel the OP puts forward two statements, categorizing depression as "adaptive", or "adaptive response taken too far." I wish to address each of these separately. Having seen what these maladies do, I believe that categorizing them as "adaptive" is a position that can only be borne from "have never seen these diseases in their full spectrum, largely responding to mild, layman's-presented versions of them." Separately, addressing the concept of them being "adaptive responses being taken too far," I find essentially tautological. Give me a little leeway to oversimplify when I say that there are two broad categories of disease: exogenous (trauma, infection - things done to us by the external environment) and endogenous (things that occur from dysregulation of human physiology). ((Aside: the above is, like all models, wrong. There are interactions and predispositions between biology, exposure, etc. I aim to use the above to illustrate a point about "adaptive response gone too far", not to overlook the full biopsychosocial model of disease.)) Calling a non-exogenous disease "an adaptive response taken too far" is a tautology. All human physiology arises from homeostasis - it's all "adaptive" in purpose, if not in effect. So all endogenous disease can be described as "adaptive response that is acting maladaptively."