OK... so I didn't expect you take the "through planes" to be literal

Are you saying you would rather have the parade of dweebs spraying tracers over your shoulder at the enemy plane??? Don't you see that is exactly what would happen if you "protected" all friendlies?
If I'm saddled up on a bandit, I really don't want to have to keep looking back to see if the tracers zipping past my canopy from 6 o'clock are "friendly" or not. Killshooter keeps that crap down.
Unfortunately, often in a tight scissors fight, someone will occasionally zoom through a snap shot of mine. In those instances, I would rather watch the friendly lose a wing to my cannons than me as he would have been much more useful staying high and watching my six as opposed to trying to grab the "free lunch". Yes, I would be willing to pay a penalty but I would still be in position for the kill... accidents happen, but in the end, the shooter is responsible for his bullets... hit a friend... pay the price be it killshooter or other methods.