When issues are separated, as in the amendment you mentioned, yes, blacks will vote according to conviction. But when it comes to voting Democrat vs Republican, convictions appear to carry little weight. It is the same with abortion. Blacks have consistently been surveyed to be more pro-life than whites. But blacks consistently vote for candidates who are pro-abortion over candidates who are pro-life. When it comes to abortion, you can't get more extreme than Obama, who has totally supported late term and partial birth abortions. But his stand on abortion doesn't matter to the average black voter, even good church-going Christians.
Local pundits agreed that there was no other explanation for the unprecedented black vote for Bush.
Believe me, if it were a proven fact that Obama is gay, he would be a pariah in the black community.