I agree that it will be a largely hostile, but probably very polite audience. If they hoot McCain down, there could be some backlash that could hurt Obama in pivotal states. Beyond that, we all assume that Obama will be the Democratic nominee, but the convention is still a ways down the road and who knows what may yet come up. If Obama has to be sacked at the convention, the Black voters will be PO’ed to say the least, and might be induced to leave the Democratic plantation this election. Then there is the argument that in the end any president is everybody’s president, and a candidate ought to act like every vote is in play, even if it is not.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus