I agree we have to all be watchful. It seems however that even partially blaming a person who enters a crosswalk with flashing lights lawfully for not taking more "responsibility for themselves" just seems callous and well, shifting blame. 
I doubt a court would even mention in a decision that although the motorist violated the law, that the pedestrian holds some responsibility.
Sure, we have to be careful. But 100% of the responsibility for this accident is with the motorist unless the signal system is poorly designed. And that is a tough one, as these things are approved nationally. Governments do not install traffic devices that are not approved.