What caused the fault? In the case that the error code encodes everything you actually need to solve the problem, sure, but having used OBDii readers I doubt that's universally the case. If you'd like to pay the mechanic more to diagnose the problem, sure. It seems it would be better to make it illegal for the mechanics to upload your data without your consent though.
Yes cause laws have been so successful at preventing unlawful upload of data.
Not in the EU, an "Event data recorder" which records speed and inputs (pedals) around the time of a crash is required by law.
Guess everyone should define what they mean by data. An error code is data. Pretty much any kind of information is data.