I understand the reason for killshooter, but there are other ways it could be handled. Instead of applying the damage to just your plane, you could apply it to both (which might actually discourage someone from cutting in front of your guns).
Alternatively, if you are worried about dweebs / spies shooting down friendlies, you could set a flag (warning - killed a friendly) the first time someone does it (in case it is an accident), and then if it happens again (dweeb/spy = yes), you boot them from the country.