I'm curious, how much self defense is acceptable?
For this hypothetical, we'll assume that I'm fairly sure that our target would like to do me serious harm and that we're both currently located in a club. Furthermore, we'll assume that if we disengage, he's perfectly capable of finding us later.
Can I open up the fight by kicking the back of target's leg? Start it with a pool cue to the chest? I mean, neither of those are likely to cause super-serious harm, nor likely to get me in any more trouble than getting kicked out of the bar. Is preemptive self-defense a thing?
I'm not gonna lie, the lesson that I took from Ender was that the same person can't both be trusted to decide when to fight, how hard to fight, and how to fight except in extreme situations (that is, where it's obvious that there should be no fight, or where it's a real fight, aiming to do serious harm).
Now, being the sort that I am, I applied it mostly to the macro level. You can't have an army deciding who to fight, or how to fight. We'll always go to the extreme if we can. I've got no problem putting a sabot round through target's torso before he can see me, that's why there's people above me telling me if I can fire on a target, someone putting me in that area and telling me I'm cleared, someone above him putting a tank in whatever country it is, politicians above that, so on and so forth.
But on the personal level, in the bar, if poor Strifey doesn't have someone looking over his shoulder, he's got to do all that evaluationing on his own (and, to be honest, I think that I've generally been pretty good at it, infrequent club-goer that I am). Is it worth it to fight at all? I mean do have at least some pride/hubris/honor to care about, plus there's the consideration of if target's planning to jump me, and that if I get the jump on him, shock-and-awe* might ensure that he and his friends no longer bother me, and man but I probably shouldn't of drank that third drink and I mean I do have that bladed knuckle in my pocket just for emergencies . . .
Effectively, lots of judgement goes straight out the window in the heat of the moment, especially when booze is involved. At least for me, I'm always going to lean on the side of excessive force to make sure that someone goes down.
The better solution is to have multiple people with you. Just like there should be a chain of command headed by civilians, there should be a friend who's a bit more distant from the situation. Better yet, there should be the designated driver. Best case, they can make a judgement, worst case, the more the merrier.
Now, besides being careful not to end up in situations like that and to deescalate if possible, as far as I'm concerned, it's perfectly reasonable and smart to be physically and mentally prepared to mess someone up if need be.
*Shock-and-awe should not be confused with terrorism, although the two share some similarities. Terrorism is the tactic of attacking civilians and civilian target to achieve a political goal. Shock-and-awe is a form of rapid dominance, now supplanting rapid dominance as the general name. You smash the opponent before he ever has a chance to react, showing him that victory ain't going to happen, forcing an early, less damaging submission, retreat, surrender, curl up into the fetal position, what have you. For the historical note, shock-and-awe focuses on destroying everything in the target military force, especially that chain of command. Leave everyone lost, in the dark, and facing superior forces with superior knowledge of the battle space. Enough to make anyone want to tie a white sock to the nearest pole and surrender to the cnn crew, you know?