Being a fan of a club or not, doesn't mean one should fight. I think it's an act of stupidity for anyone to take up a fight with someone they know or barely know all because they are not a fan of the same football club and their perspective about their club doesn't align.
However, this fighting between a club fan that happens once in a while is an act of immaturity. A mature person can't fight or point fingers at their fellow beings all in the name of being a fan of a club that doesn't know or care about your existence. Fighting should be the very last thing that should be in the mind of a true fan of a club. Fighting for a club doesn't show dominance of a club above the other, rather it shows a foolish attitude of that being
Yes immaturity is needed in the game of football fansto avoid such. Though even matured people also argue seriously among themselves. And all what is to be done is to avoid such when the argument leading to quarrel and fight. There are time those arguments are interested to do. Mostly pre Match argument is interesting because when one of the team finally wins then the loss team will be silent and others will be happy and celebrating.
Everyone mindset is not the same so if you notice that the other person is angry then we have to leave the argument.