What's vulgar about biochem explanations of psychological disorders is that they assume that the chemicals are the cause - that once you've identified some chemical configuration or process, you've hit the bedrock first cause.
Situational and societal causes of mental illness should be given their due, but scrutinizing the biochemical end of things certainly makes sense considering the varying genetic propensity toward depression and other disorders (I think for depression twins share a 60% likelihood of depression when raised apart). Regardless of the situation or the societal organization, depression is more likely to effect these groups and that has to do with the biochemical/genetic factors, how their particular brain circuits regulate emotion and mood.
Also I think there is a misperception about how easily some disorders can be attributed to our system of social organization. I frequently hear from lefties and others (including on this list) that attention deficit disorder has to be caused by something in the environment, whether it's poor parenting, acceleration of media, or the drive by the managerial class to discipline the popular majority. A psychotherapist I know who has actually dealt with ADD/ADHD patients for 10 years and who believes few disorders actually need drug treatment has concluded drug treatment is the best option in dealing with this issue, it's analogous to "eyeglasses and poor vision" from what he's experienced. The environmental factors may exacerbate the individual's problems stemming from the disorder, but I'd be very surprised to see environmental solutions alone significantly alleviating the symptoms of this highly genetically influenced disorder.