Let's be clear here: James' argument is not that the social/human environment is more important than natural selection; rather, he contends that natural selection is no longer occurring in the human species. The former claim is at least debatable; the latter claim displays a willful ignorance of evolutionary theory and research.
[WS:] I agree that the claim whether human/social environment is more important than natural selection is debatable, because (i) it is very difficult to specify the criteria of importance and (ii) those two are not mutually exclusive, and social environment can affect natural selection. However, I would not want to be construed as some kind of downplaying the role of neuroplasticity in the individual's ability to function in the social environment - the damage caused by adverse social conditions, neglect, improper socialization etc. (especially in the childhood) can permanently handicap the person's ability to function in a society for life. This is, btw, one of the strongest arguments against incarceration of juvenile offenders I can think of.
So from that standpoint, the negative effects of social environment and socialization are more likely to adversely affect the chances of survival than natural selection (which is not the same as being more important.) This rests on the assumption that individuals that are poorly integrated to society have lower chances of survival, which is not the same as a lower probability of having offspring.
As to whether James ignores evolutionary theory - he can certainly speak for himself, but I do not think that it is what he claims. He seems to argue that humans acquired ways to neutralize the effects of natural selection through social development and technology in the ways that animals could not - which is not the same as denying the existence of that selection. In the same vein, the fact that we can eradicate the incidence of certain diseases does not deny the validity of bacteriology claiming the effect of bacteria on the human organism.
Wojtek