I don't really see the point of an atheist rally. Atheism shouldn't be organized and dogmatic like religion. It should merely be the absence of religiosity.
But at the same time, I'm all for black atheists being more vocal and open, as I think religious orthodoxy is a substantial hindrance to our growth.
Regarding organizational aspects of atheism, it's kind of a fine line, because like I said, you don't want it to be dogmatic and structured. But at the same time, not religion per se, but certain strains of religiosity can have a deleterious impact on the world, and it should be combated by rational thought in the arena of ideas and policy.
I'm not interested in telling people their God or Allah is just as false as Zeus or Ra. They can believe what they feel. Where things become problematic to me is when to use a few examples:
-Supporting immoral and self-defeating pro-Israel foreign policy because they want to clear the way for Jesus to return.
-Stymying the implementation of life-saving stem research because destroying embryos is killing souls.
-Denying the realities about global warming/climate change because of misplaced belief that only God can steward the Earth.
-Bigotry against homosexuals rooted in scripture.
-Denying the reality of evolution and trying to sneak creationist bullshyt into classrooms.
So these literalist, fundamentalist strains of religiosity can be problematic in variety of ways on a macro-level, and rationalists, be they atheists, agnostics, deists, or just liberal-minded religious folks should confront that, and some form of organizing around reason and science could be prudent. I'm kinda going off on a tangent a bit. But the basic point is it's not always as simple as "let's just all respect each others' beliefs" if you have any vested interest in maintaining a secular society that values human rights, remaining technologically and scientifically competitive with other nations, or simply just crafting a better world.