Why is it a matter of dogma for you that all differences are due primarily to culture or environment? Is it really your contention that some people aren't born with innate talent, while others are born innately incapable?
For instance, I have zero musical ability, not due to lack of trying. If I was adopted at birth by a virtuoso musician couple and immersed in music, there's no doubt I'd still be terrible at it.
Similarly, a black child with an IQ in the 80's adopted by a wealthy, educated family and given every opportunity in the world will still have an IQ in the 80's. He might do better socially because he won't be drawn into a life a crime (or is less likely to be), but he won't become talented by osmosis.
I think exDemMom is not as exDem as she thinks.
It is an article of faith among marxists/leftists that Man is malleable and perfectible, the notion first being promoted by 18th Century precursors of Marx, like Rousseau, Saint-Simon, Hegel, and others. If people are malleable and perfectible, then the only reason why they are not currently perfect is because of an imperfect environment. If the environment is made "perfect", though the action of the State, then a society of perfect people will result.
The alternative viewpoint is that people cannot be made perfect by environment.
People may strive to improve, and thus improve themselves within limits. Environments can be improved to allow individuals to reach their potentials. HOWEVER, we reach a point of diminishing returns, where spending ever more money on improving the environment produces ever less increments of improvement in the people targeted.