"I ought to be able to walk around town in fine clothes without a stab vest. However I would be very foolish to do so and I would consider myself partly at fault if I got knifed."
The only difference I can see between your analogy and mine is that the normal prudent person is currently expected to lock his car but is not expected to don body armour in public. And it seems to me that though we're stuck with "you're stupid if you don't lock your car" because that's Just How Things Are and have been for a long time, normalising body armour would on the whole be bad for everyone and should be resisted despite any temporary advantages it might offer in some situations to early adopters. Likewise any other defensive behaviours that aren't presently "normal" but could be made so by social pressure: what do we actually gain as a society by making them so?
Well I agree with that, but mainly because stabbings are very rare, but petty theft isn't.
Are you saying you shouldn't take any measures to protect yourself? You could easily say that you shouldn't have to move to primary at a pinch point (as car drivers shouldn't overtake you there anyway), but we do - in order to protect ourselves.