Hate to sound like a broken record here, but in terms of the chain of causation it doesn't have to be an either or choice. It is entirely possible to have deficiencies in design, production, regulatory oversight, corporate culture, maintenance, training, or what have you - all at the same time and all making a contribution to the accident. Maybe instead of this endless debate regarding the primacy of one particular causal factor over another, we should rather try to identify ALL the casual factors and agree that all of them need to be addressed.