Depends on the situation.. Is it a seemingly defenseless woman, alone, being harassed to the point where she can't call for help, cornered, being spit on and bullied by numerous people to the point to where her life is threatened? If so, sure, I support her defending herself via any means necessary.
And ultimately, the crux of this case really isn't about whether or not this is legal. It's pretty clear that throwing popcorn does not cause someone to fear for their life, so the shooter will likely serve time.
The issue here is that legal or not, if you confront someone you just might get dead. And when you're dead leaving behind a widow and child, it's not going to matter whether or not it was legal.
THAT is my problem... That a father, husband, is not only so selfish and daft as to pull his phone out in a theater, but he also is bullying a poor old man and throwing popcorn at him. I place that blame squarely on the young buck who initiated this entire thing and left his family without a father.
Again..... Legal or not, that sort of behaviour is not tolerable and if you act that way towards a crazy you could very well end up dead... Gun or no gun.