This is painful to watch and the crowd was no more than mildly respectful; there is nothing wrong with a crowd booing a speaker when they disagree, and the crowd did boo at points.
Romney did clinically review the facts that African-Americans are doing more poorly under Obama's failed policies but the crowd was not receptive to that reality. He never really got off the ground since the audience was so dead but he could have given the speech more emphasis anyway. Also, although he touched on traditional marriage he did not hit home that Obama favors gay marriage. Among Christians this point would have hit an audience much harder. In the ranks of the NAACP traditional marriage may not be such a strong selling point.