I've been on the autobahn a couple times, don't recall seeing the circle-with-slashes sign more than a handful of times, usually pretty short stretches too IIRC. Could be just the road I was on.
Anyway the facts are pretty indisputable that fuel economy goes to hell at speed and crashing at speed is more likely to result in your death. The little mpg calculators on the web only go up to 85mph. At 150 mph you might get about 7 mpg. A colossal waste.
Still, people are free to drive 100+ mph on the autobahn, pump over 300 pounds of carbon into the air per hour, and endanger their own life and others.
I am free to be not impressed.