Metaphysically speaking, the three terms materialist, physicalist, and naturalist point in the same general direction. Quibbling about them might actually be a useful exercise in conceptual analysis, and it's easy to start distinguishing them, but my philosophical views can be variously interpreted or described as materialist, physicalist and/or naturalist, depending on the context. The general idea is that the natural universe, physical nature, is what exists. This is not necessarily a "reductionist" view. Today I want to say some really basic things about humanism, that I see as incompatible with (my view) physicalism. From my physicalist point of view, nature can be as magical and mystical and mysterious as you find it, or as it might be. My claim isn't that we understand nature or that nature is some sort of deterministic mechanism. My claim is more modest: I claim that whatever nature (the natural universe) is like, human nature is like that. Humans are not any sort of miracle, in the sense of an exception to the ways of nature (whatever those may be). Humans don't in any way "go beyond" nature. They are in fact humble creatures on an obscure planet in a universe packed with life.
Two points following from this programmatic declaration of mine. First, while it is legitimate for all of us to be motivated to some extent by ethical, social, and spiritual concerns, don't assume that the one you're calling a "materialist" has somehow forfeited that high ground to you, the humanist. In addition to honestly believing the metaphysical propositions that I espouse, I certainly am also ready to defend them in ethical, social, and spiritual terms. Physicalism looks to be the environmentalist position, for example. I am also prepared to defend the proposition that physicalism is the most spiritual metaphysical position, as opposed to, say, metaphysical dualism about the mind and body. I may be wrong in those views, but don't assume that I concede any of that part of the conversation to humanists: theirs is not obviously the most ethical position.
The other point is that there is a great deal of humanism around, and some of it is pernicious I think, for example in so far as it blocks progress in psychology, neuroscience, and related areas. The Chomskian linguists, for example, are the descendants of a mind/body dualist tradition, indeed self-consciously so. So this is a central idea in the "cognitivist" section of the animal mind book.