You're clearly attempting to be rational and even handed but it is pretty hard to take it seriously when you're stating AFL & common sense in the same sentence.
Given your earlier analogy to car incidents for example if two drivers were having a drag race and both crashed hurting each other I don't see the authorities letting them both off because they've been injured equally. Part of the penalty in any of these issues - particularly with head high bumps - is surely the deterrent factor of the penalty. You don't achieve that with players getting off if they hurt themselves as well.
But, if you have a car accident, and you are 100% not at fault but kill or injure someone completely by accident, you are unlikely to be charged (this implies the other party are at fault).
However; if you are breaking the law and have a car accident, you are charged no matter what the outcome. But, the outcome of the accident will drive the severity of the charge.
In this instance there has been an outcome (Rohan being concussed) as a result of Durdin playing within the rules, yet he has still been penalised.