[BRAN]

laws and their enforcement are a necessary evil, because (some) people can't behave.
Now the question is...who wants access to a "private" car and why.
Looking at the accident statistics for Germany, speed is interestingly NOT the TOP reason for e.g. fatal traffic accidents. And most fatal accidents DON'T happen on the Autobahn (without speed restrictions).
Most fatal accidents happen on rural and city roads due to disregarding the right of way (for whatever reasons). That annual report is very interesting and often leads to the conclusion, that discussions over speed restriction are OFTEN politically motivated.

A general speed limitation for the Autobahn won't really help to reduce the numbers of fatal accidents (which declined in the last 50 years over 75%, contrary to the fact the that there are milions more vehicles on the roads nowadays). Will it help to reduce the CO2...marginally yes. Will it make the Autobahn safer...marginally yes.
If the cars are maintained and regularly inspected...they are pretty safe these days, capable of running at much higher speeds than 30 years ago.
What really kills is not speed, but distraction (e.g. texting, or phone, or browsing your internet capable car computers) or a knowingly violation of laws (speed, red lights, right of ways...you name it).

so speed limiters for certain areas might be okay, but can only help so much.