The problem with using a purely neurochemical explanation like this is the rates of these disorders differ dramatically between societies and within societies geographically, demographically and over time. It is clear that the United States in particular is, especially in recent years, churning out unprecedented numbers of severely psychologically ill individuals. The idea this is solely due to previously undiagnosed individuals or otherwise not representative of a sickening society is difficult to support.

Frankly we have spent too long acting as if mental disorders could not possibly have anything to do with ones surroundings, upbringing and life in general, when it's beyond obvious that they have very much to do with those things, as well as genotype/phenotype/etc. We've used this idea that it shames individuals to suggest that the actual problems they deal with could contribute to mental damage in much the manner they can physical damage, which is simply dogma masquerading as science.

In fact, using purely neurochemical explanations denies people's humanity and lived experience, denies that we are sentient humans not some organic robots that need an serotonin oil change and some dopamine transmission fluid.