But why self-defense only with guns? And against terrorists?

Randy Barnett raises an interesting perspective in The Unorganized Militia Once Again is Needed

Here is the cold hard fact of the matter that will be evaded and denied but which must never be forgotten in these discussions: Often —  whether on an airplane, subway, cruise ship, or in a high school — only self defense by the "unorganized militia" will be available when domestic or foreign terrorists chose their next moment of murder. And here is the public-policy implication of this fact: It would be better if the militia were more prepared to act when it is needed.

I think that his point could be expanded to include common criminals (i.e. without a political agenda) and viewing self-defense by means other than only guns. The police cannot be everywhere and it infantalizes the population to tell people that they should not take action in self-defense even when the police are not present and are not likely to get there in time. Maybe there should be various levels of self-defense courses, appropriate to age and circumstance, offered across the country. Would muggers et al simply escalate their own offense? Or would they be deterred, recognizing the decreased likelihood of success and even their own survival?

What would a national crime policy look like that took seriously the fact that the police cannot be everywhere?