I think this ignores the argument the high speed limit people make which basically boils down to "sure some people will die or get injured but its worth it because driving faster is fun"

I believe you, but do you have a citation?

Autonomous vehicles following proper signalling before lane changes can be safe at arbitrary speeds (see Autobahns working at all). Humans, we should limit passing speed to roughly ~5 mph delta between adjacent lanes and leave it at that.

Humans with adequate following distance in the entire lane can probably manage 10 mph delta. I routinely travel dozens of miles very safely at ~80 with the flow of traffic (including the cops), and been stressed out at 55 in the carpool lane through stop and go traffic in the right-hand lanes due to on ramps/offramps.

What happens at 76mph?

> my ancient truck, steel bumper, and class 5 receiver hitch will not be badly harmed by your plastic grille

I've been rear-ended in my truck, and the receiver punched a nice hole right through the radiator of the guy who hit me. Definitely fucked his car up way more than it did my truck ... except man, that is definitely one of the hardest impacts I've ever felt in my body. I now appreciate how hard the head rests really are, despite looking a little soft. I think I'd rather have crumpled crumple zones and a new truck next time.

>it's customary to leave a path in the left 'passing lane' for any traffic that wants/needs to go faster than you

It's not just customary in many (most?) states, it's the law. People who sit in the left lane are the problem.

> it's customary to leave a path in the left 'passing lane' for any traffic that wants/needs to go faster than you.

A custom that (where I live) is becoming more honored in the breach than the observance. It makes driving very much more dangerous.

In Britain they have a sardonic nickname for people who do this: CLARAs. "Centre Lane Residency Association".

> If cars match speeds across lanes, it impedes faster traffic.

I think this undersells it a little. It does not just impede faster traffic, when the lanes are pacing each other it makes navigating harder -- simply switching lanes is more difficult. The highway moves so much more efficiently with a small but steady difference in speed between each lane.

We have a lot of freeway speed limits that are holdovers from the last oil crisis decades ago. Cars have gotten quieter, smoother, more capable, to the point where 55 mph is kind of hilariously slow. When the legal speed limit does not reflect what most drivers think is reasonable, then we can stamp our feet and insist that the law must be right, or we could redesign the road or adjust the speed limit to more closely reflect conventional wisdom.

Road capacity does not increase with speed above 50 km/h on urban roads or 70 km/h on highways. Following distance scales with speed, so more speed can actually mean fewer cars per unit of time.

In theory, braking distance scales quadratically with speed. In practice, people leave less room on highways, because they rely on others driving predictably, but spacing still increases faster than linear.