If we are talking about guns as a preventive of crime, then wouldn't open carry be more effective than concealed? Say you are in a store, waiting in line with your glock on your belt for everyone to see and a robber walks in with intent. If the robber saw someone with a gun wouldn't they then look for another place to rob?
Plus, if you are legally entitled to carry, why hide it? It would seem only someone who either illegally obtained the firearm or has illegal motives for carrying would want to conceal.