In this day and age of better blends of fuel, efficient cat converters, high fuel efficient vehicles and 7+ geared transmissions being the norm, I absolutely agree with you that the EPA and tree huggers should have zero say in what speed limits should be. During the fuel shortages, that was a knee jerk reaction to drop everything to 55, but that was also the day of big V8s being the norm in the family grocery getter. Post Clean Air Act, we can actually see further than 10 miles and even LA has a good view on a normal day. So that argument we're on the same ground at.
I'll even say many states, especially in the east, have speed limits that are far lower than necessary. I live in the land of 80 MPH limits on interstates, and most all secondary roads are all 70 MPH. Each state gets to set their limits, and some have more sense about that than others. Vehicle safety is better than ever, and we're coming to a point where even congested areas can bump up their speed limits, especially in areas where the flow of traffic is almost always higher than the posted speed limit is. But, that's not my point here.
My point is the disregard for the law and the safety of everyone else on or near the roadways. If traffic is flowing at a certain speed, even if that's a fast speed, accidents are reduced because the relative speed is all the same. Folks entering the roadway know to expect someone to be moving that fast, but when someone is traveling in excess of that expectation it is dangerous as it is difficult to recognize that excessive speed when looking straight onto an oncoming vehicle.
The roadways are dangerous enough as it is when folks are obeying the rules. A huge deal is made out of one airline passenger death in almost a decade, but in that same span over 30k are killed on the road every year, with over 25% attributed to speeding in excess the posted limit. These aren't Greenpeace stats that were dreamed up, this is NTSB's data that's empirical.
https://www.ntsb.gov/news/events/Pages/2017-DCA15SS002.aspx
So with that many deaths and injuries, it's obvious two things need to happen. First, states need to analyze their roadways that have habitual speeding offenses and increase their limits if applicable. Second, the punishment for speeding isn't bad enough to detract violations. I don't like fines in most cases, mainly because they're severely punishing to the poor while being a near-zero influence on the rich, but everyone gives a shit about their freedom. Negligent vehicular manslaughter doesn't carry a severe enough punishment to the offenders, but the pain and loss to the families is no different than if committed by a serial killer, dead is dead and there's no getting their loved one back. We applaud someone getting the needle for shooting someone in cold blood, but that asshole that causes a multiple car pileup with fatalities because they either couldn't leave earlier or in general didn't give a fuck about their fellow citizens to obey the law gets off with far less of a sentence. Both are a threat to free society's endeavor to life, liberty and happiness, only difference is negligent is just another way of not giving a fuck if you kill someone or not without really wanting to kill someone. There's little difference in the end result.
My seven days behind bars for fifteen MPH over, sure, that's brash on my part as well as them paying for their sentencing, gruff "Pit talk" if you will... But I'm dead serious when it comes to DUI offenses because that kills just as many as speeding does, yet is a flagrant "fuck everyone else" when someone drinks and drives. It's too commonly accepted that one can beat the charges with a good lawyer to make a plea deal to reckless driving and attend some bullshit classes, another example of our broken justice system.