My oh-so-brilliant and ethical academic friend was asked how to deal with a sensitive issue of capitalization by another academic recently. I found her answer is so thought-provoking, I am sharing it here.
Question: If I am speaking specifically of a black or white pastor, do I capitalize Black or White? What about if I'm speaking of the Black church or the Black Church?
Answer: Oh, this one is a big ol' can of worms! Some people capitalize Black but not white, perhaps on the theory that the capital "B" affords a certain respect to a more-or-less unified ethnic group, whereas "white" does not refer to any particular ethnicity. So, for example, it could be argued that the expression "the Black church" or "Black churches" suggests the existence of some shared characteristics -- ritual practices, theology, inculturation -- among those churches, perhaps as a result of the history of people of African descent in this country. But the parallel expression "the White church" does not usually evoke a similar idea, in fact it sounds odd: because there is no identifiably "white" way of worshiping.
Some folks capitalize "Black" but not "white" because the latter refers to a dominant -- and therefore paradoxically invisible -- grouping, whose hegemony dictates the "normal," from which identifiable ethnic or racial groups can be recognized as deviating -- or less pejoratively -- differing. So the "different" groups get capitalized (e.g., Latinos, Asians) in distinction from the norm, which is "white." In this view, "Black" has as much claim to capitalization as "Latino."
More recently, the advocates of the field of White Studies -- which is in part the study of white hegemony and in part the study of particular ethnic strains within white America ("America" being a term I usually render "United States", because America is bigger than the U.S. -- but that's another kettle of fish!). So these folks, in an attempt to indicate the illegitimacy of a white norm, capitalize "White" to indicate its place as one among many groups, rather than as the true north from which all others deviate.
Some folks prefer to render both "black" and "white" in lower case, thereby avoiding the problem. I think this is common practice among many sociologists.
I try when it's not too cumbersome, to talk about people of African descent. This is more inclusive than African-American, which excludes, e.g., people from the Caribbean living in the U.S., and more precise than "Black" -- which can also refer to people of South Asian descent -- especially in the British and British-influenced world. But "churches composed of people of African descent" is a mouthful, and doesn't really convey what I imagine you mean by the Black church, i.e., churches founded and led by descendants of African slaves in the United States. By the way, the one expression I wouldn't use is "Black Church," unless "Church" is part of a particular denomination's name. (For example, my own denomination has changed its official name to The Episcopal Church, abbreviated TEC.)
Not very helpful, eh? In my own writing I usually capitalize "Black" but not "white." This is partly because in a U.S. context, "Black" refers to a group of people with some historical, linguistic, and cultural unity (an albino African American is still Black), whereas "white" does not. The main reason, however, is to signal to Black readers a generalized respect and acknowledgment.