Earlier quoted context omitted.
Except it isn't random. Some cops just look for the fastest cars while others will look for out of state license plates. And some will even go as far as basing it off of the demographics of the driver. We would never tolerate a speed limit that allows difference races to go different max speeds, but allowing selective enforcement by cops enables any cop to do this.
Speed is just a red herring anyway; as you said it's all about selective enforcement. I'd rather there were NOT any speed limit enforcement at all UNLESS there's another infraction. Even more ideally self-driving cars would just save us. However until then I'd prefer that laws like Washington State's 'keep right except to pass' were strongly enforced.
I recently drove from Tuscon, AZ to Cleveland, OH. All 8 states I drove through have them, but somewhere around Misouri signs get smaller and less frequent, and they stop being strictly enforced. Ohio recently started pushing to enforce this law. It seems as exits get more frequent and less lanes are available, (road maintenance in 4 season territory costs a lot, so there are more 2 lane highway spans than 3-4) lots of drivers decide that the speed limit +x MPH is fast enough for everyone, FU if you're behind me. I'd guess it added +/- 8 hours to the trip.