I've got, well, a worry regarding the "necessity" requirement on the legitimacy of self- or other-defensive force. I don't really work on this stuff, so it's entirely possible that there's an easy, pat answer to this worry. Anyway, I'd be interested to hear what you all think.
It's traditionally thought that defensive force is justified only if that force is necessary to prevent harm to oneself or another. Or rather, what's traditionally thought is a specification of this. For we need to draw a distinction between two types of cases in which the use of force is unnecessary.
Type #1 (the type you were probably thinking of): Biff attacks Marty. Marty uses force to fend off Biff's attack. But Marty could have escaped by skateboard instead, and so Marty's use of force is unnecessary.
Type #2 (the type you may not have been thinking of): Biff attacks George at the soda shop. George uses force to fend off Biff's attack. But George could have avoided Biff's attack by not going to the soda shop in the first place (and let's say George knew that Biff would be at the soda shop at that time, and would fly into a violent rage upon seeing George there). So George's use of force is unnecessary. Let us suppose, for the sake of contrast with Type 1 cases, that once Biff attacked, George could not have avoided harm except through self-defensive force.
According to what we might call "classical" Anglo-American criminal law, defensive force is impermissible in Type 1 cases. "Stand your ground" laws are, then, a deviation from classical A-A criminal law. But the law traditionally regards defensive force in Type 2 cases as permissible, assuming other requirements — proportionality, imminence, etc. — are met.
In the aftermath of the George Zimmerman trial, I wondered whether the law might should be amended to count Type 2 defensive force as unnecessary in the relevant sense. After all, Zimmerman didn't *have* to approach Trayvon Martin; he could have just driven on and maybe called the police if he was so inclined. I posted something to this effect on Facebook, and received plenty of "likes", which I take as evidence that others concurred. (I'm not on Facebook any more.)
On reflection, though, I rather doubt that my and others' intuitions about the Zimmerman case were driven by our adopting this more restrictive conception of necessity. Instead, I suspect that most people who suspected Zimmerman was in the wrong really thought so because they believed one or more of: (a) Zimmerman's killing of Martin was disproportionate, (b) The killing was not in self-defence, (c) Zimmerman did not reasonably believe that it was in self-defence, (d) Even if the killing was in self-defence, it was in response to *Martin's* use of force in *permissible* self-defence, and so was itself impermissible.
At any rate, I think it is wrong to classify defensive force in Type 2 cases as impermissible-because-unnecessary. It seems to me that George's response to Biff above is appropriate. Or suppose that a female undergraduate has just successfully fought to force a campus club to admit women. Let us suppose that, if she attends an end-of-year party at which members of this club will be present, she will be assaulted. And let us suppose that her credence in this is justifiably high. She attends the party — perhaps partly out of determination not to give in to misogynist hostility, perhaps out of confidence that she can defend herself — and repels an assault with proportionate force. It does not seem to me that her use of force is impermissible-because-unnecessary.
Anyway, those are my intuitions about Type 2 cases. So suppose we wanted to uphold those intuitions while hanging on to the traditional necessity requirement (i.e. the one that pertains to Type 1 cases). What differences between the two case-types might we cite? I'm at least initially attracted to a roughly-drawn view that we might call "the world is your oyster" (or "TWIYO" — trademark and apparel pending). On this view, you have the right to be anywhere you want, subject (maybe) to the property rights of others. Doesn't matter if it's a rave at an abandoned warehouse, a neo-Nazi rally, or the "cheap" seats at a Philadelphia Eagles game. The criminal law should never force you to choose between avoiding certain places and placing yourself at the mercy of attackers by going to those places. The law would be forcing this choice by counting defensive force in Type 2 cases as unnecessary, and so it oughtn't to do so.
But recognize that if proscribing defensive force in Type 2 cases offends against your right to be where you want, so does proscribing such force in Type 1 cases. In our imagined case, for example, Marty would be forced to either flee or just sit there and take it as Biff attacked him. The law and Biff's aggression would conspire to make it impossible for Marty to safely stay where he was.
Now, maybe you think there's an important distinction making it impossible for a person to *go* somewhere safely, and making it impossible for her to *stay* there safely. But why? What could justify placing a higher value on people's ability to venture out into new places than on their ability to stay in one place? (I find it hard not to think of the post-Bennett literature on acts and omissions here. Imagine a world of conveyor belts, etc., etc.)
I would think the answer would have to take the form of a claim to the effect that the goods to be attained by going to another place are higher or more valuable than the goods to be attained by staying where one is in the face of a threat. We liberal elites romanticize exploration, expanding one's horizons, experiencing new pleasures, broadening one's perspective, and so on. It's less clear to us what's so great about standing up to aggressor when flight is an option. We would look askance at Marty were he to claim that his social status would suffer by standing down from an asshole like Biff, or that his sense of himself, of the boundaries that separate this self from others, of his personal integrity would suffer by allowing Biff's aggression to push him around the world-space.
But I'm leery of this answer. First of all, there are some Type 2 cases in which goods one would forgo by avoiding the would-be aggressor are not so great. I mean, suppose Biff only hangs out at the soda shop from 4:45 to 4:50 PM; what would George lose by avoiding being there exactly then? Secondly, there are Type 1 cases in which the goods one would forgo by fleeing are great on any measure. Suppose a guy assaults me just as Springsteen brings my wife up on stage to sing "Thunder Road", dedicated to me, on our wedding anniversary. Finally, and a bit more seriously, I'm reluctant to dismiss claims of the sort I imagined Marty making in the previous paragraph. Some people's sense of self-respect, of integrity, etc. may indeed depend on standing their ground. And the reputational effects of running from an aggressor may be very real, even if not in my social circles. Of course, you may say that these goods are not worth, say, an aggressor's life/limb. Perhaps not. But then neither are the goods in many Type 2 cases (on any reasonable reading of this "worth" claim).
Now, obviously one response to all of this is to say that the criminal law must, for reasons of "followability", draw sharper lines than the moral law draws, and so we should just continue treating defensive force as "unnecessary" in Type 1 cases and as "necessary" in Type 2 cases notwithstanding the putative difficulties I've raised. But of course it is partly an empirical question just how much moral complexity it makes sense for the law to reflect.