I've read his earlier book Vision of the Anointed which I suppose addresses much the same topic.
But my point remains that you can still believe innate human nature is good and be a conservative or that innate human nature is evil and be a liberal.
What side of the fence you fall on in the nature/nurture argument has far less to do with it than your proposed solutions.
Vision of the Anointed was Sowell’s polemic.
In “Conflict”, he’s more balanced, examining what he calls the “unconstrained vision” vs the constrained or tragic vision of mankind. It was really amazing how he wrote it with no bias toward one or the other as “right”.
However, he DOES assert that your solutions will invariably flow from these base assumptions.