The availability of the drugs allows for:
1) Doctors to have a ready, reliable quick solution to the patients' problems.
2) Patients to convince themselves and doctors that they need those drugs.
Also, it is true that predisposition doesn't mean expression.
However, when speaking from an evolutionary perspective, we have to talk in terms of statistics over long periods of time. If the potential is there, and we are of course assuming that there is a potential for higher risk of depression, then it is likely that it will be expressed.
My point was never that all depressed people are genetically inferior; in fact I said that in agreement with the article, low to moderate levels of normal depression as a reaction to difficulty can be advantageous. My point is that, like all other genetically related disorders, there is a clear disadvantage that puts their genetic line at risk, and that this is partly what allows species to evolve and survive.
Perhaps, given a more effective drug and its implementation in healthcare, as well as a stronger awareness of neurocognitive disorders, we can better prepare future generations to deal with depression to the point of avoiding severe or chronic bouts.