For the record, I'm in favor of CCW for properly trained/prepared citizens, and I'm opposed to "no carry" zones for same. I won't argue against the position that a lawfully armed citizen might have made a big difference in several of the recent tragedies. I also, professionally, try to stay current on our scientific understanding (or lack thereof) of violence risk factors and perpetrators. That being said:

"the vast majority of mass shootings in America's recent history (last 50 years) have been in "gun-free zones" or "weapon-free zones". The stats aren't even close to being the other way around."
I'd appreciate being directed to any credible studies which address that conclusion. Not necessarily doubting the comment...just would like to have the actual data.

"I believe the empirical evidence is overwhelming that these cowards prefer to attack unarmed people where they gather..."
Is there any data regarding what "these cowards" think, or prefer? The FBI, DOJ, and Secret Service Behavioral Sciences units have the most data... and I can't find anything which says this about the perpetrators' thinking processes or motivations.

"Removal of the 'guns banned here' signs probably would have totally prevented the incident in that specific venue. "
Is that so? If the killers have such aberrent thinking as they appear to have, could taking down signs have "totally prevented" the incidents? I know a lot about psychosis and delusional ideation (NO..not from my personal experience with the voices in my head, folks...) and it isn't that simple.

Many (hopefully all) of the opinions expressed in this thread come from (hopefully) sane, reasonable members here. So they sound like just good sense to me. The problem is we non-crazy minds are trying to understand the thoughts and motives of some pretty crazy killers: we have little hard data to help us do that, at this point. The assessment or prediction of threatening behavior and who will become violent toward others is imprecise and subject to significant error. At this point in the scientific understanding of these issues we are guessing, and there is currently no unchallenged data regarding the factors which increase vs decrease risk. I'd like to take some comfort in the assumptions that allowing CCW and elimination of no-gun signs would dissuade deranged killers, but I can't. Perhaps armed citizens could quickly kill the killers once they got started on their spree - but would we prevent them from getting started?