Black History Month is not just for black people. In an ideal world, there would be no need for a dedicated month to mark black history -- and the significant contributions that blacks have made around the world -- because it would be on par and as well-known as History, i.e. the mainstream history that many of us learned in high school. I don't know how history was taught when you were in school, but in my school our teachers skipped over the chapter (yes, only a single chapter) on blacks in Canada and North America more generally.
Sure, I understand that there's much to cram into school curricula, but when we skip over or elide significant aspects of our country's past, we demonstrate what -or who - is important or unimportant in our society. These omissions -- which affect, of course, not only blacks, but also Asians, native peoples, and various other ethnic groups (women too lest we forget) -- skew our view of the world and lead to erroneous assumptions. If a child, or an adult for that matter, only learns about the contributions of those of European descent, it's unlikely that they will consider that people of other races or ethnicities also played a significant role in building our country. How can you be expected to know and understand the full spectrum of history if you've never been given non-traditional examples? To put it another way, if you never saw the colour blue in your lifetime would you know that it even existed?
I don't see Black History Month as revisionist in any way; the aim isn't to rewrite history to artificially raise the ranking of black contributions; the aim is to bring to light or to the surface the people and events that were forgotten or that were purposefully buried in the annals of time. Also, Black History Month isn't designed to elevate black culture over white culture. One isn't better than the other. In fact, neither history or culture is separate or distinct because it's a shared history. The concurrent stories on both sides of the coin are what make our shared past. Black History month isn't just my month, or your month, or the month of a friend of yours. It's ours.