For me there is a simple list of conditions where I view it light enough on the moral grey scale to do something like that:
> Are they Nazi/Neo Nazi/Neo Conservative?
> Are they chavs?
> Are they invading my country?
> Are they threatening my loved ones?
> Are they putting the life of someone else in danger?
> Are they attacking me with enough equipment to put my own life in danger?
> Are they mooks working for someone who has taken the life of someone close to me?
> Are they responsible for the death of someone close to me?
> Do I genuinely believe that their existence contributes nothing to our existence and serves only as a parasite on society? (see: Chavs/Bill O'Rielly)
Personally I find killing to be a distasteful act, one of last resort, however in a kill or be killed situation I doubt that there would be much of a delay, if someone was trying to hurt my family or friends then there is no question that I would intervene with force, however I always attempt (and have done in the past) to resolve situations where someone has to go down without the use of weapons, this is because I do not like using guns or blades, I prefer unarmed fighting, granted the person trying to kill me may think differently, but the collection of recovered weapons I have amassed tells me that sometimes taking a knife to a fist fight is not the right way of going about things, especially if your opponent actually knows how to use them fists
In a situation of extreme emotion I may bring myself to the act of killing someone, but this is SERIOUS emotion, like someone who has killed a friend or family member and I have just pursued and taken him down, otherwise I am happy to turn people over to the UK legal system, I never EVER hit someone while they are down, Hitler or not, when someone is on the floor and cannot defend themselves then you do nothing, maybe help them up so you can carry on the brutalising, but never curb stomp (well, unless he has a gun that he had hidden and is now aiming at you!)