“The reasonable fear of great bodily harm is enough, I believe.”
You might be right if there was reason for fear of great bodily harm. I don’t think that throwing popcorn goes anywhere to that level. And if you or I had shot someone for throwing popcorn on us we would rot in jail for the rest of our life.
In and of itself that sounds reasonable. I've asked what the popcorn thrower's intention was. Did he turn a verbal argument into a physical assault? Did he do so in order to provoke retaliation and use that as justification to beat the cop senseless? I don't know.
On a different thread there are claims that the shooter threw popcorn first. That puts him into the position of possibly having initiated the physical confrontation. Would it then be fair to believe, in that case, that the ex-cop was the one trying to provoke a retaliation, knowing that he could then try to claim justification for shooting? If so, his culpability rises dramatically.
There is certainly a sharp legal boundary between not shooting somebody and shooting. My point is that there is also a sharp legal boundary between a verbal argument and physical assault.