A CCW isn't a badge; only police have the obligation to 'go forward' to make an arrest. If one, as a citizen, is headed toward a crime in progress to try to stop the crime one way or another, that is an additional risk (personally and legally) that could turn out as badly for you as it too-often does for the police, who generally have qualified immunity from personal liability.
Think like a jury would - what would 12 reasonable people from your community believe was a justified set of actions? What were your options to avoid a use of deadly force? Were you precluded by the circumstances from any other course of action? What some folks on this forum think might just fall outside what the 12 folks representative of the community would decide.
Due note that the citizen who most famously, appropriately used deadly force to stop a mass shooting, Stephen Willeford, a NRA firearms instructor at Sutherland, Texas (the church massacre) used an AR-15 on a man dressed in black kevlar as he was reloading a Mini-14 after methodically firing more 100 rounds inside the church next door. That is hardly a shooting in a crowded mall with ambiguous identification of good v bad.
My opinion is that shooting folks is best avoided whenever possible. Minding your own business generally is good as well.