The issue here is that most of the time something like half of people are speeding and some of the time literally everyone on the highway is speeding. The people who set the speed limit set it with the goal of causing a certain kind of psychology on the people driving, not because "past this point your car is going to lose control and kill everyone", and the law is then defined to follow the signs (which expect people to go over) and not the reality. It is just all fundamentally broken, as you can't fix it by changing the signs or defining a "true cap" as that would also break the psychology parts and lead to drastic differences of relative speed. The result is that no one truly cares about speed limits as defined (nor should they) and so police have immense discretion to use "you were speeding" to nab almost anyone, which is giving the police departments (who are optimizing for their budgets) and police officers (who are often applying flawed stereotypes as their model of criminal behavior) way way too much power.
"past this point your car is going to lose control and kill everyone"
Actually that is one of the reasons for the speed limit being what it is. Part of the speed limit is determined by the reaction time and stopping distance of a typical driver. That's not you per se, but it has to work for everyone. While a fit young person driving a 2017 Mercedes might feel they can safely drive much faster with all the modern safety features of their car like ABS, traction control, ESP, etc, the speed limit has to also work for an 85 year old in a 1981 Toyoto Corolla that has no safety features, tyres 0.1mm above the legal minimum, and the reaction times of an asthmatic snail.
That is a popular fiction for why the speed is set lower than the design speed that someone young and fast would expect, but the real reason is to figure out how to make it so that the people who drive based on the feel of the road and the people who drive based on the speed limit have the mean of their distributions at the same place, minimizing the speed differential between people on the road (which is what is extremely dangerous).
> Traffic engineers believe that the 85th percentile speed is the ideal speed limit because it leads to the least variability between driving speeds and therefore safer roads. When the speed limit is correctly set at the 85th percentile speed, the minority of drivers that do conscientiously follow speed limits are no longer driving much slower than the speed of traffic. The choice of the 85th percentile speed is a data-driven conclusion -- as noted Lt. Megge and speed limit resources like the Michigan State Police’s guide -- that has been established by the consistent findings of years of traffic studies.
Just because you can break a law and it usually works out, doesn't mean that what you're doing isn't a crime.