Instapundit on the question that a lot of people should be asking but aren't: Does a society in which gun ownership is permitted and encouraged, run a greater or lesser risk of this kind of attack?
I would say far less of a chance. Imagine this:
You are a small (10-15 people) band of gunmen looking to disrupt a city. If you go to a country where only the police and military can carry weapons, you can prepare for a response by taking hostages, barricading yourself and preparing for a police seige. Your tactical and strategic picture is relatively straight forward, pick soft targets, control access and control your captives with executions.
But if you are that same small band in a country where you are not sure if you are going to have one or more individuals in your target who not only carry weapons, but know how to use them, you have a far different tactical situation. You have to not only worry about police/militia response, you also have to worry about either a coordinated or uncoordinated counterattack from your immediate targets. People with their own weapons need not even be coordinated in their response, simply putting a few rounds into a gunman drastically alters the tactical picture, reducing the number in your band and putting at risk your own plan.
Think about that for a minute.