Physical fighting... Well, the entire thing completely depends on the situation. Beating up on someone for being gay or for an insult like "You suck" is pointless, but... We're only human, after all. If somebody makes a really personal comment, it's the natural reaction to get angry.
And as for cases like World War II, well... Those go without saying as times where fighting was morally justified, if not necessary.
And as for cases like World War II, well... Those go without saying as times where fighting was morally justified, if not necessary.