The difference is that no black person has ever gotten kicked out of his house by his mother for being black. Not many black people can "hide" being black. And black people were brought to this country which was already founded on questionable circumstances.
Gay people are worldwide thought of as an aberration. Heck as I mentioned, even some parents think their kids are [insert non-derogatory adjective] because they are gay. Civil rights and "gay rights" are nowhere near the same.