well... Since I live about 800km due North of you (~480mi, and a bit North of the border) the repercussions for me would be quite different.
If I told the police I was going to my neighbour's house with a firearm I would definitely be arrested, and they may send a cruiser by to check out the domestic dispute.
Anyway, that all plays a part too. Since I know that there is lots of hunting around here and firearms are readily available, that plays a big factor in making the decision in the first place. Know your environment.
Interesting statistics quoted there too. Are they real, and can I quote them? Is there also a number of unsuccessful defences, or numbers on unarmed defences? I have been casually looking for more stats on attacks and whatnot.
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I'm curious about the numbers, too. I've never seen an explanation for the numbers that some pro-gun rights organizations claim that makes sense to me. I'm a cop, and to reach those numbers, it sure seems like I should be taking a lot more assault/robbery/other violent offense reports where the intended victim scared off the assailant with a gun than I am. Of course, it could be that they don't report the attempted crime, but than I've gotta thank them for leaving the criminal running free without so much as telling the police...
I'm not a fan of private citizens intervening with guns, simply because it's all to easy for that gun to end up in the hands of the criminal -- and because it radically escalates the danger to the citizen. Police officers shoot other plain-clothes officers from their own agency because of miscommunication and misidentification; how much greater is the chance that a civilian will be the victim of such a mistake? I do carry off-duty, but the main reason is to defend myself and my family -- not so that I can intervene in a situation.
If a person absolutely feels that they MUST intervene in order to prevent death or serious bodily harm to another, and that they can do so reasonably safely (defined as with acceptable risk to themselves and anyone around them), then they absolutely must be prepared to obey the police when they arrive. There is absolutely nothing more frightening to me than to be told something like "caller reports her husband left the house with a gun. husband is wearing..." as I respond to any sort of call, whether it's an alarm or a report of an attempted homicide in progress. I don't know if that guy is going to mistake me for a bad guy; I don't know if he has any real idea of where he's shooting or what I may be doing to respond to his call... And that applies even if the guy's a cop. The way my agency does things may not be the same as the way his does them.
One last point... If you feel you absolutely must intervene instead of following the course of wisdom and calling it in and letting the cops handle it -- do so decisively. There's no room for half measures. You're not paid to simply restrain and arrest someone. And when it comes to serious or deadly bodily harm -- neither are cops; we shoot to stop the threat. That's a polite circumlocution to avoid saying that there are no warning shots, there's no shooting to wound, and that if we're shooting -- someone's probably going to get killed.