The opponent is too dumb or too helpless or too new to know any better. In this instances flaming shows poor judgement skills and disregard to your lesser gifted brothers and sisters. It's just wasting precious energy on unworthy person. The dumbass doesn't realize that she needs to work on the right to be flamed and that just because she says some idiotic thing, it doesn't mean that anyone will pay attention to her. People just love to give themselves undue credit.
Flame wars are for idiots.
There's no art, no skill and no thought in it - just a bunch of idiots calling each other names. You don't want to be associated with idiots. Flame wars draw in people who have no control. In these precarious conditions, one has poor judgements and clouded mind. Flaming requires pure heart, clear mind and cheerful disposition.