For all the horror of the killings at Virginia Tech, there have been several incidents in the past where the death toll from a deranged gunman could have been just as high or higher — except for citizens who were also armed and fought back. Read a great summary of these incidents here.
As the author notes, in most of these stories, the media was conspicuously silent about the role of firearms in preventing further killing. Now, why, do you suppose, they would leave out a little detail like that? Hmmm?