Generally a killshot happens when two or more aircraft are shooting at the same target, i.e. the target is outnumbered. Killshooter allows for the outnumbered target to benefit from the outnumbering opponents' overzealousness at getting the kill before their comrades.
If there was no killshooter, the idiot in the back spraying away would hit his teammates in front and kill them, thereby evening the odds a bit for the target in question. But no killshooter also leads to the certainty of intentional griefing, so this is not really a desireable situation in the game.
No consequence for landing hits on a teammate (op's suggestion) means the target remains outnumbered despite the idiot in back spraying. There is absolutely no disincentive for all 8 cons behind him from unloading all their weaponry hoping theirs is the magic bb that will find the noggin. This then means the target is well and truly boofed.
Or, we have the elegant solution of the current killshooter. Idiot in back sprays, hits the teammate in front . . . and the idiot evaporates, leaving our target in a slightly better state than he was in before because now only 7 cons are chasing him instead of 8. This is the most "fair" result to target while not allowing idiot to intentionally grief his teammates.
The sad result is that occasionally it isn't your own idiocy that gets you killed, but rather poor SA or plain dumb luck. But that is a minor annoyance given the greater goals.
