Good question. My guess is as follows:
Per the NHTSA [1] alcohol, excess speed, and not wearing restraints are the top three causes of vehicle-related deaths in the US in roughly equal measure (although alcohol edges out the other two). The German autobahn infamously doesn't have a blanket speed limit and is about as safe as other European highway systems. To me this means that a case can be made for high speeds on public roads in the interest of expediency (though, for cultural reasons, I would not personally make it for the US). I can't, on the other hand, imagine endorsing road sodas or not wearing seat belts. In other words speed is only contextually dangerous while driving drunk and not using safety equipment are inherently bad which is why I'd imagine the latter two have been legislated.
Anecdotally I'd be much happier if more attention was spent on enforcement against bad driving behavior like tailgating, weaving, failing to signal, driving drunk, and running traffic signals than speeding. Nearly every brush with death I've had on public roads has been due to these, not somebody doing 95 in the fast lane.
[1] https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/...