In a 1v1 situation I try to give a courtesy check if nothing else. But in a furball situation with multiple bandits it's really hard to look at the situation and say "gee, is this really fair to them?"
Last night an enemy pilot complained to me about diving into a 2v1 situation (he was the 1) and shooting him down. Really...in the MA...after he'd already gotten me more times than I'd care to count. Anyone who doesn't expect to be overwhelmed by numbers in the MA on occasion is really kind of a whiner in my occasionally humble opinion. I'm of the belief that the MA should be flown as close to wartime conditions as possible. If you want sportsmanship, fly in the DA.
As far as exiting the fight goes, it may be frustrating for the opponent but exiting a fight when the odds are not in your favor is just common sense. Besides, exiting is a skill in and of itself, as is trying to get into a vulched field. If I'm hit, low on fuel or at a serious numerical or energy disadvantage...well I ain't afraid to run from you. Besides, it only works about half the time.