Professor Jacobson has asked me to address whether such an act would be lawful as a justified act of self-defense. I’m on a flight now using airplane WiFi, so I’ll make this quick. (Before I go on, however, I should point out that Professor Reynolds has added some important context to his pithy tweet, and these later comments can be found at the link above.)
In short, one would apply the usual five elements of a self-defense justification to evaluate such a use of force against others, just as in any other instance of self-defense. Those elements are, of course: innocence, imminence, proportionality, avoidance, and reasonableness.
Don’t screw around and go read this post by Andrew Branca now.