What if someone was armed?

All these shootings lately.We (rightfully) complain that if a law abiding citizen was armed it could have been prevented.But what would happen if it was?The person who shoots the ailant could be percieved as the ailant in all the chaos and get shot themself by the police.The person could get sued by the "victim"'s family.Sure people would be saved,but what about the person who saved them?I'm not saying I know the answers to these questions,I'm just asking what you think