Of course, me being a philosophy student, I have some qualms with your conclusions and method, but that is not to say that I think you have not done a great job with this post. Most importantly, I don’t think anyone can claim that humanism follows from naturalism in a strict logical sense. Rather, I think it is more nearly correct to suggest that humanism seems to follow from someone’s desire to save the idea of morality, in the face of the death of dogma and the supernatural. The assumption is that morality is a sacred (i.e. worth preserving) teaching and/or ideal of sorts. And there are lots of reasons to stand by this premise–many of which you address by way of describing the benefits of being a moral person in a moral society. Many philosophers are content with accepting the promise of the morality idea. Some are not–being fairly poor read in this department, I can only name Nietzsche here, but I am sure he is nowhere near standing alone.

I think you are right to suggest that more thinking about naturalism often causes a person to reject certain beliefs about the foundations of religious morality. But, ultimately, I believe alternative beliefs about morality tend to draw more from religious morality than anything that might follow from the facts or condition of naturalism. This would perhaps help explain how relatively simple it is to go from a church-goer to being a conscientious socially-minded believer in people. Again, this is not necessarily a bad thing. However, I personally am interested in thinking about what happens when human societies take significant breaks from the lessons of A.D. religious morality. Who is to say that a a-moral life is necessarily worse? Even if aspects of morality seem to have natural brain-related causes, it might be that these drives and judgments can be displaced in favor or some alternative scheme.

At any rate, I think this blog post of yours does a great job making humanist naturalism out to be a far more defensible belief than any sort of belief in the supernatural.