This also seems to be the mentality of rape apologists.
When something bad happens, they blame the victims for not protecting themselves enough.
Then they go out and start waving their piece around, and act all offended when people take their earlier advice and interpret it as a hostile act.
So, apparently, to prevent mass shootings, we need to foster a mentality that if we see people walk into crowded areas with loaded weapons, we should not immediately assume they're dangerous.