Great discussion here.
But here is how it looks from my point of view.
The moral issue is: If I feel threatened, I will defend myself with deadly force, and not feel guilt.
The legal issue: A jury might not see it as self defense and find me guilty of some form of assault, manslaughter or murder charge.
The resolution (for me): If I truly felt threatened as I mentioned in the Moral issue, I would believe that if I don't defend myself I will end up dead or, through luck, only severely injured. If I even consider not defending myself because of what the legal consequences might be, perhaps I don't feel all that threatened after all.
I read some pointers about home defense. The thing to say to the Officer is "He said he was going to kill me and I believed him". Well, if I truly believe they are going to harm me, I will act. If not I will attempt to withdraw until I am safe or cornered with no resort but to defend myself.
In any case, if i believe the threat of death or severe harm is imminent, I will defend myself and hope my skill is enough that I will live to defend myself in court if it comes to that.
There is no doubt that a when a flash mob harasses someone, it is not to give them a good laugh or warm feeling, it is to bully them, frighten them and make them feel threatened. If they do a good job of it, they pay the consequences no matter what their true limits might have been.