Other than what the OP said, I would have no intention of tackling a shooter. There might be some remote chance that I might find the opportunity to attack a shooter from behind, if the right circumstances presented.
I look at it this way - I owe the greatest duty of protection to my family and myself. I will help others, but not at a great risk of getting myself killed. Others need to provide their own protection for self and loved ones. Just because some of us carry guns, doesn't turn us into cops or deputies. Myself, I am neither armed, nor trained, to defend anyone not right near me.