Very valid point about the shooting chutes. However, there is not enough information to make a reasobable 'judgment' for lack of a better word.
First... If you have bailed out and opened your chute, you are immediately able to do the .ef command or "end sortie" from the clipboard. There is no need to just hang around and watch the fight. You do not have to be on the ground for a successful bail. Which then leads into the second point....
If you have bailed from the aircraft and are just floating around enjoying the view, there is only three reasons why. You are "spying" reporting back enemy locations to friends -- thus a valid strategic target. Or, you are close to an enemy airfield and are floating down to spawn camp the runway and shoot the pilots in the head of aircraft trying to take off. That also makes you a perfectly valid target. Or, you could be coming down over a friendly town that the enemy are trying to capture, you can (as a chute person) enter the maproom and kill troops as they enter and prevent the capture. This also makes you a strategically valuable target.
So, if you were 10 miles from nowhere and NME-a came around to shoot you just for the entertainment of ensuring your "kill", he is further dropping your score modifier and is a piece of crap.

But, I must ask, why were you just hanging around for him to return and kill you?
The only other valid argument I can make for the chute killing is people who bomb and bail. Yes -- If I can find their chute I will shoot them into ashes, collect the dust and spread it out over the open open to ensure that they never materialize again.
But back to the original point, I do NOT as a rule of thumb, shoot the chutes unless they are coming down on my airfield -- or the above mentioned bomb-and-bailer.