There are a load of factors that would help decide who was in the wrong. I don't think it's impossible to design a piece of software which can work it out. I've had a few races ruined because someone was riding my ass at T1 and didn't see me brake early to allow the person in front space, therefor pounding me into the barrier. Here are some examples of things to consider in an automated system:
1. Relative speed at moment of impact. Generally the slower car isn't going to be at fault, unless they're driving in a crazy fashion (see point 2).
2. Actions being taken at moment of impact. If you're braking, you're at least trying not to hit someone else. If you're accelerating, it's more likely to be deliberate. Obviously steering towards the other car means you're likely to be to blame (that one would be hard to figure out though). Possible exceptions would be sudden braking on open areas to cause the trailing car problems (see point 4).
3. Part of car involved in impact. If the front of one car hits the side or rear of another, the chances are that it's not the side of the car to blame. Likewise, not too many race incidents are due to someone reversing into someone else (see points 2 and 4).
4. Relative position on the track at impact. This one is really only relevant when someone is re-entering a race after pitting or going wide. If someone is off the line and hits someone on the line, it's probably their fault. Collisions where both cars are off the track should not be considered, since you're pretty much at the mercy of physics when in the gravel on racing tyres.
There are probably more that would help as well, but these are all that are jumping to my mind at the moment. Obviously no automated system is going to be perfect, but with enough variables it should be possible to have one which is right the vast majority of the time.
I do agree that once proper damage, aero physics and collision detection systems are added, this will probably not actually be so necessary, since the fear of destroying your bodyword/tyres/suspension will force people to drive fairly.