99% of the time, I'm shopping alone. As long as I know my family is safe, I'm under no obligation to help others. With the realities of a justifiable shooting potentially costing me and my family everything, I'm going to pick and choose my battles carefully.

To the O.P. question, If I'm in a position to ambush a bad guy- and I have to know it's not just a brand new, clueless gun owner bringing his recently purchased AR into Walmart to return it- but a legitimate bad guy, then yes, I'd take him out.

On the other hand, if I'm armed with my usual carry, a .38 snubby or a an LCP, and he's got an AR on the other side of the store and there are dozens if not hundreds of panicked people running right thru my line of my fire, I'm getting out of Dodge. I'm not going to chance: going to jail and being sued for accidentally shooting an innocent fleeing bystander, or getting shot by the responding cops who saw me with a gun stalking someone in Walmart, or getting mowed down by the bad guy for trying to help a bunch of ungrateful Democrats who are going use the occasion to ban guns while my family tries to put their life back together.

If I, or my family is in immediate danger, all bets are off. I will fight to the death of one or both of us.