I've thought about your question, and there could be a couple of very good answers:
1. A LOT of the rabble that support 0bama are "Bandwagon" morons; they support him because they think it's cool. Walking out shows them that it's OK to tell the commie to Go To Hell;
2. Maybe there were limited tickets available for the event and by getting a ticket it prevented some weak-minded moron from attending.
PRAY FOR AMERICA!