I reapat my litany here: if you want to use a handgun to defend yourself and your own family in your own home, that is your right and your choice. You will need a degree of training and solid nerves if you want to do it right.

To defend others in a crowded public place, especially one where people are panicking over the sound of gunshots or the sight of dead/injured people lying bout, then you will need extensive training, experience, nerves of steel, high situaltional awareness and a sound sense of judgement to do it successfully.

That set of skills is not easily acquired and beyond the reach of many.