I don't think it's so much free market, than realistic.
Its nice to believe that posting a speed limit means everyone will abide by it. It's also great to believe that everyone breaking the limit can be caught and he) d to account, every time.
I too, using many forms of transport these days follow the rules set for me, but see many others who don't.
Telling people smoking kills doesn't get the message across, they still smoke... Drinking, eating bad foods, not exercising. Driving is no different.
Some are susceptible to having things impressed upon them, speed kills etc. Many others are simply too selfish and cocooned in their private bubble to bother paying attention.
Limits can be lowered, signs can be put up everywhere, bit enforcement is the key. Hence the community speed project suggested.
As for 20mph limits... My road is 20mph and has speed cushions which zig zag down the road. A car travelling at 30mph on the same road without speed cushions is LESS likely to have an accident IMO. Rather than 20 and swerving about all over the place.
Enforcing school zones, halving the speed limit when lights are flashing etc (like the US) is more appropriate
Blanket 20s are silly.