The black movement of the 1960s was separatist. It led to the formation of black caucuses in the unions, black studies departments, etc. There is a tendency to assume that this movement has been a failure because the black community remains impoverished. It is obvious that only an integrated working-class movement can accomplish large-scale economic and social reform.
However, it is shortsighted to assume that an all-black gathering serves no useful purpose. I am acquainted with some of the Marxists who work with the Brecht Forum in NYC, who I am sure will attend this gathering. They are looking for ways to hook up with like-minded activists around the country. If they can make this connection, then the gathering will prove useful. Black activists face the same problem as Marxists. We are isolated and require organization. One of the reasons people participate in Doug's list or mine is that it is a way to make connections. There is absolutely no difference with respect to the Black Radical Congress.
It is inappropriate to open the door to white participation. Feminist groups, gay groups, etc. have the right to choose who can attend their gatherings. This is not reactionary. It is actually democratic, insofar as it expresses majority rule.
I am quite sure that the mass revolutionary movement of the future will look like some sort of coalition of various movements of the oppressed. The black movement historically has been the backbone of progressive politics in the US. One of the reasons the student movement has been so relatively quiet is that the black movement has been quiet. If there is an upturn as a result of this congress, every movement will benefit, including the labor movement.
Louis Proyect (http://www.panix.com/~lnp3/marxism.html)