". . the complex interactions between genes and the environment that lie at the heart of many mental disorders."
We don't need to understand these "complex interactions", not that it would help much, even if we did.
We need to understand something much simpler, which we - even the experts - don't see, because we don't WANT to see it, not because we can't.
It is the fact that the genetic basis of human nature evolved in a natural environment VERY different from the artificial environment of civilisation we live in today.
If we were the "rational animal" we (especially academics) suppose ourselves to be, we would have shaped this environment to serve the best interests and well-being of society at large, but we are not and we didn't. We are far more a "rationalising animal" which rationalises state, economy and status quo to suit our own personal, narrow and short-sighted, self-interests.
Society has been shaped over centuries by its ruling elites and their most favoured clients to serve their own personal self-interests, at the expense of society at large and of its long-term survival.
See BLOG in which I elaborate in these ideas.