People who want to get rid of speed limits say they're a vestige of the past. Modern cars are much safer than anything made before. Besides, the cars that would truly take advantage of an autobahn-like system would be engineered to handle those kinds of speeds. Drivers should be able to make decisions for themselves—Germany proves people are responsible enough to figure out how fast they can drive.
Supporters of speed limits say the autobahn can't be replicated in other places without rebuilding major infrastructure. The autobahn was designed with no speed limits in mind—not so much with American highways. American infrastructure can't handle higher speeds.