I do wonder whether bad guy's knowledge of CCW folks has much effect. In theory it would seem it does but at same time some bad guys just seem hell-bent on commission of their crimes regardless.
I doubt somehow that Cho in the VT episode would have paused for long had he known there could be armed resistance - he was IMO too far ''gone'' as a head case to worry - after all he was already decided on taking his own life probably.
But ... and here is the percentage .... I do feel that in ''gun-free'' zones .. AKA ''easy pickin's'' areas .... the disincentive to trying on any stupidity could be diminished, even if seen as a possible up to a point.
I try (with difficulty) to put myself in the planning mode of a bad guy .......... and have to say that the prospect of return fire would indeed make my decision way more difficult, if not untenable.
Bottom line - it almost matters not whether deterrence would apply - the final deal is, the ability of CCW individuals to be able to ''answer back'' - and probably at a much earlier stage than when a gunman has ''carte blanche'' and it's open season for his mayhem.
I am only saying what we have already said and written - a la ''Nuge'' - which is that gun-free zones do NOT keep folks safer. I know too that the ''choir'' is alive and well on CC