I'm perhaps the least qualified person here to suggest the cause or causes of the accident (though most accidents turn out to be a sequence of problems not a single factor). I've read the report in full twice and (I think) every post so far on this thread, carefully.
Eleven unconnected people were killed. Whether they were unlawfully killed is for the Coroner. As an engineer (and low hours PPL) I understand Newton's Laws as they apply to aircraft. Whether the aircraft had structural 'failure', power 'failure', instrument 'failure' or whether the pilot had mental or physical 'failure' it is perfectly predictable that a large mass will continue in the same direction unless another force is applied.
The eleven people were killed because a large mass travelling at high velocity, laden with kerosene smashed into them. That was clearly the 'CAUSE' of the deaths. Certainly all the pilots on this thread will follow the argument that the vectors of all display aircraft should be calculated before the display is approved. It is very easy to do mathematically.
I suggest that there have to be special and compelling reasons to approve a display that has a proportionate chance of anyone being harmed if the pilot or the aircraft fail at any stage in the display.
One poster earlier mentioned Farnborough. Good point. Maybe that's an exception, not my call. Of course Blackbushe is practically in the circuit as is Lasham.