[dsfyu404ed]

In a theoretical world that doesn't include ticket revenue and "think of the children" speed limit is a function of road design and some reasonable average vehicle/driver/conditions. They are an output rather than an input. You don't just assign a speed limit. It's based on the road and condition. In the real world US speed limits outside of urban areas are laughably low for reasonably attentive drivers in clear weather and light traffic.

In an well maintained sedan there is no reason why one cannot drive at triple digit speeds on the vast majority of the US interstate highway system if traffic conditions are light enough to permit it. The biggest risk from traveling much faster than other traffic on limited access highways is rear ending someone who changes lanes without a signal.

Speed limits exit not because "dumb things are inevitable" but because dumb things are far less common when traffic is moving a close to uniform speed and providing a suggested speed that most drivers find reasonable most of the time helps traffic flow more uniformly and safely.

Furthermore, the rules of the road provide massive redundancy. That's why a margin for error exists. By going much faster or slower than other traffic you are getting rid of the margin. If you're going fast you're depending on other people to not move unexpectedly. If you're going too slow you're depending on other people to be driving slow enough and paying attention enough

The person who changes lanes without signaling while going 50 in a 60 where everyone goes 70 can only claim the moral high ground over the person who rear ends them because they were going 80 and couldn't compensate adequately so long as the latter party doesn't have a dash cam.

[onychomys]

I think it's important to remember that the national speed limit of 55 was put in as a fuel saving measure in the 1970s. Drag increases in a non-linear fashion with velocity, so you don't just use twice as much gas to go 110 than to go 55. In a world where we worry about carbon output (either from your ICE or the natural gas plant that makes your supercharger electricity), that's a very real reason why one should not drive at triple digit speeds on a highway.