I agree that discrimination of any kind is wrong, but don't you think that comparing the plight of atheists (today, and in America, as that's where the billboard was put up) to the historical plight of African-Americans, as the OP did, a bit... hyperbolic? Hell, in many parts of the South African-Americans are still generally treated as inferior. And I've never heard of anybody in this country being lynched for being an atheist (though I'd like to point out, before people start throwing up links to news stories, that it wouldn't surprise me, but it unquestionably doesn't happen to the degree it happened to blacks). I myself have never faced any sort of discrimination for my lack of belief.