Negatives stemming from the free will myth
Economic and social inequality
The widespread assumption of libertarian freedom, which states that an individual is at bottom self-made, works to justify and excuse huge differences in material well-being and social advantages. Those that fail economically, on this understanding, fail because of a willful refusal to apply themselves or follow the rules. Since it was their bottom-line choice not to get ahead, they deserve their misery. Likewise, those that succeed deserve their riches, however excessive or disproportionate, since they made themselves who they are. The huge inequalities between rich and poor are tolerated partially because they are thought to reflect differences in metaphysical merit derived from the differential exercise of free will.
Ineffective social policy
To the extent that economic and social inequality are believed to result from human choices unaffected by surrounding conditions (the definition of libertarian freedom), such inequality will be perceived as the natural outcome of self-chosen individual differences, not anything that could or should be remedied by social policy. Social programs and income redistribution, therefore, will be only thought capable of operating around the margins of what is essentially up to human free will. The free will assumption, therefore, disempowers and defeats interventions to reduce inequality in advance by implying they cannot be effective, or that they somehow infringe our right to ultimate self-determination. (Of course if we really had libertarian free will, our self-determination couldn't be infringed upon.)
Positives stemming from inclusive naturalism
The end of metaphysical merit
Inclusive naturalism shows that an individual's economic and social success is entirely a function of family status, innate talents, and numerous other environmental and biological factors, not free will (see Rawls quote below, note 1). Successful individuals can no longer claim that their riches are deserved in the deep, metaphysical sense of having created themselves and their success ex nihilo. Nor can those who end up on the bottom be blamed for their failure on the grounds they could have chosen otherwise, given the circumstances that obtained. Social and economic inequality will be understood as the luck of the draw, not a reflection of metaphysical merit. This will undercut justifications for inequality based on the notions of deserved entitlement and deserved failure.
Egalitarian social policy
If success and failure come to be understood as entirely a matter of environmental and biological conditions, not a reflection of self-created will, then social and economic inequalities can no longer be defended on the grounds that they are somehow deserved. This will undercut support for laissez-faire social policies that permit huge discrepancies in wealth and opportunity, and increase support for interventions that improve both opportunities and outcomes for the disadvantaged. Although incentives must still exist to encourage hard work and risk-taking, they need not result in a grossly skewed distribution of goods. Inclusive naturalism will shift the justification for having a reasonable standard of living from what's deserved to what's needed to avoid suffering.
 "It seems to be one of the fixed points of our considered judgmentsthat no one deserves his place in the distribution of native endowments, anymore than one deserves one's initial starting place in society. The assertion that a man deserves the superior character that enables him to make the effort to cultivate his abilities is equally problematic; for his character depends in large part upon fortunate family and social circumstances for which he can claim no credit. The notion of desert seems not to apply to these cases" (Rawls, p. 104, A Theory of Justice).