Opportunity: The RNC was scheduled way in advance. It was known that there would be huge protests. Our government has one of the lowest approval ratings in U.S. history. It is extremely unpopular, so protests were only to be expected.
Motive: When the Communist Chinese suppress dissent and we do not, it makes them look bad. It appears to many that we have a more democratic form of government than they do. Allowing dissent in the U.S. gives people all over the world, including China, the idea that dissent is appropriate and should be tolerated. When people see news about open dissent in the U.S. and brutally suppressed dissent in China, it stirs up anti-Chinese sentiment. This does not make the Chinese government happy.
Means: The United States has a huge trade imbalance with China and, at least according to what I've been reading, is so deeply in debt to China that it could not fund its wars of aggression for another day without being able to borrow money from China. Since the U.S. ruling party (parties, for those who may think that our pro-war government consists of two ruling parties rather than one, although I don't think anyone would say that there is an opposition party) has pre-funded our wars of aggression until 2010, they need to keep that line of credit from China open. It is interesting to note that the Republicans voted to pre-fund the wars just in case a Democrat took office or there was a Democratic majority in Congress that might wish to defund the wars, while the Democrats voted to pre-fund the wars so that even if a Republican took office and there was a new Democratic majority in Congress who wanted to defund the wars, they would not be able to do so. In any event, due to the need to keep borrowing money from China, China is in a position to call the shots and tell our government what to do. For the U.S. government to disobey a direct order from Communist China would end the wars in Afghanistan and Iraq tomorrow, as we wouldn't be able to pay for them, no less fulfill our commitment to keep paying for them.