At http://GUNLAW.PRO I discuss how firearms training can bolster an estate plan. But does this apply in reverse? Can having an estate plan aid in self-defense? While probably not a factor if you are defending self only (self-preservation instinct), or someone very close to you (object of your planning), having an estate plan in place to take care of your family may be a significant factor in "deciding" whether to help third parties not as close to you, perhaps even strangers. Most likely, there will be no time to "decide" at all, and the lack of an estate plan, giving you lifetime peace in the knowledge that your family will be adequately provided with sustenance, will cause hesitation. In a gun fight, hesitation can be deadly.
The military places a great emphasis on estate planning, and so does the "religion of peace" under Sharia law, which is quite detailed on the subject. You may recall the recent "flotilla participants" executed wills before departure.
How likely is it you will face this? Back in the ol' Republic, when times were more peaceful, stable and prosperous, it was estimated that 25% of mass murder shooting sprees were stopped by private armed citizens. The concern also applies in other more common situations (e.g., local stop n' rob), and many predict more terrorism on these shores.
Of course, sometimes it is good to hesitate before engaging where engaging would be foolish. You need to think through these issues in advance. Here is a great discussion of some things to consider:
In a free area where you are legal to carry your pistol, again the choice is clear. Good guys can intervene in times of danger and victimization secure that if they act properly, they will probably be fine afterward. That is the reality of why places where gun laws are lax are far safer than places where gun laws are strict…because good guys are not afraid to be good guys.