The problem with Secretary Condoleezza Rice (as opposed to Ambassador Susan Rice) and her choice to decline in the face of this 50 student protest is that it sets the bar very low for the next protest against a non-liberal speaker. Will it be 40 that gets Senator Richard Lugar banned for voting Republican on the occasion. Will it get Charlie Christ banned if 30 protestors rage because he appeared in support of Senator McCain’s 2008 Presidential Campaign?
At some point in this progression, it would appear that a single malignant doofus can cancel out any non-flaming liberal speaker if the school administration is sufficiently weak-kneed, which means 95% apparently!
Yes, a single "no" vote will be enough to cancel an event. Since such votes will be coming from every side, only the most bland events will be ever permitted. The government does not want the population to be politically aware on its own. It is not yet possible to outlaw political activity, but it is possible to use other laws to block it1. In the end, all political opinions that the population needs to have will be coming from the radio and TV that are under control of the government.