No, there was not a hero citizen with a gun to save the day. The perpetrator opened fire with an automatic rifle iin the crowd at point blank range and was eventually brought down(not killed or critically injured) by the security guard there. But to touch on your point, that's a very dangerous way to think. The point of these Congress by the corner is to be a down-to-earth, no big government event so people can get a sense that the officials they elected aren't just in the background, hiding from the public.
What I have a huge issue is Palin's chart:
http://tpmlivewire.talkingpointsmemo...crosshairs.jpg
Where she uses cross-hairs to identify Congress members who voted yes for Medicare. What does propaganda like this say to a nutjob?