"That means they are set were the speed most people feel comfortable driving is faster than the posted limit - in other words in places where the limit is wrong, as on average drivers pick a reasonable speed"
I disagree. I live on a street that is entirely residential, in a district that is mostly residential, but has a highway feeder entrance ramp nearby. Two roads, mine and the one parallel get not only a disproportionate amount of traffic, but higher speed traffic than other streets in our area. Yes, there are larger roads bracketing the area that were designed to take the traffic and allow a higher speed, but they have traffic lights. So, we get the "greedy, speedy" types that must rush through our street, killing dogs and cats, honking at kids and adults on bikes, and breaking the speed limit in a residential area. We need a speed camera(s) to stop this traffic.
Or.... here is a (libertarian) solution. When I was a kid in the early suburbs, there was a nacent suburb being built on the hill beyond our house. The only way in to the suburb was past our house. Every afternoon, just after my dad got home from work, a resident from up the hill came flying over the rise before our house and dropped into a lower gear as he went down to the bridge over a little creek at the bottom before the hill and then up the hill to the burb. Dad flagged him down one day and asked him, in the name of the pets and children in our set of houses, to slow down and quite driving like an asshat. He didn't . So, a week or so later, dad came home and grabbed a fencepost from the pile beside the driveway and stood by the side of the road. I watched and listened as the sportscar came barrelling down the road and over the rise dad dropped the fencepost into the road and stepped back behind a tree out of sight. The car hit the fencepost, jumped up, out of control landed sliding into the ditch and rolled into the empty lot across the street. Dad grabbed the post, sauntered over to the pile and threw it back on it and went into the house without even a glance at the sportscar or its driver. Problem solved.