There were many discussions about this precise matter.
Frankly, from what I observed in those discussions, there were some good points made by all sides, but none of them were enough to present a real alternative to the kill-shooter system we have.
There can be such mixed variables concerning the dangers of kill stealing and kill-shooters, that it's really hard to side with one argument - ie. a Bf109 corners an enemy Spitfire down at deck, and during maneuvering, a friendly Zero decides to join the fight.
That can be considered both:
a) The frdly Zero is a hotshot wannabe jumping into your line of fire
b) You weren't good enough to finish him off as early as possible - if you can't land the final blow, someone else gladly will
It depends on what point of view you stand at. If I was the Bf109, I would feel a) towards the frdly Zero.. but if I am the frdly Zero, then I would feel b) towards the frdly Bf109.
Also, it can be said that both the Bf109 and the Zero are at a fault in that they failed to acknowledge their surroundings, and failed to communicate. Accidents like that happen in real life, too.
Thus, in this particular issue, it is hard to set a real 'standard' on who is right. Currently, the KS promotes the harsh consequences of and forces the players to communicate, acknowledge their surroundings, and consciously try to avoid KS situation voluntarily, all the time.
In my situation for example, if I were in a Bf109, and I corner a Spitfire down low, it is obvious that it will take some time for me to land the death blow. I, of course, will try to do best as I can, but were I to see many frdly Spits otw to me, and see that they have an intent to engage, then I'll just let off a sigh and pull out of the way. Well, better luck next time.
Or, were I in a Bf109G-10 with 30mms, chasing a La-7, and a friendly P-51D is also chasing him close to me, I would have to look back and see if the frdly P-51D can get a shot in - I have to go within 200 yards or so to really land a hit with 30mms, but the frdly Mustang with .50s can try a shot at least 300 yards further than me. So, what I do is try to get to the La-7 close as possible, but in a slightly offset flight path so I give some room for the guy behind me to try a relatively safe shot.
Yes, I don't get many kills this way, but I try to as much as I can to avoid unpleasant happenings by checking what is going around me. I rarely ever get, or cause a KS this way. Maybe if more people can find the truth in this cooperative alternative through Kill Shooter, then they may also find that KS is a reasonable solution.