The potential consequences of mass surveillance come to mind.

While it is true that many people do speed, that doesn't make their speeding "the real speed limit".

I've driven behind drivers driving 25km/h in a 40km/h area and not stopping for pedestrians at a crosswalk with right of way (if somebody jumped out elsewhere, they'd probably just run them over at 25 km/h), whereas I always do even if I am driving at 45km/h because my foot would be hanging over the brake near areas of low visibility (like intersections) or near crosswalks or with pedestrians near the road.

Your braking distance is largely a function of your reaction time (attention + pre-prep + reflexes), and your car performance (tyres, brakes) on top of the speed, and speed limits are designed for the less than median "driver". You obviously have most of those under your control, but the speed is the easiest to measure externally.

The obvious counter is that I could be even safer if I also drove at 25 km/h, but it would take me much longer, I'd hit many more red lights, so I might stop being so attentive because I am going "so slow" and taking so long (maintaining focus is hard the longer you need to do it).

However, measuring individual performance is prohibitively expensive if not impossible (as it also fluctuates for the same person, but also road and car conditions), so we use a proxy like speed limit that is easy to measure.

Which is a dangerous line of thinking, as everyone thinks they're above average.

Speed limits are also, to some extent, designed around physics. Higher-speed accidents have more kinetic energy.

Anyway. I come from the UK where we've had camera based enforcement for aeons. This of course actually results in people speeding and braking down to the limit as they approach the camera (which is of course announced loudly by their sat nav). The driving quality is frankly worse because of this, not better, and it certainly doesn't reduce incidence of speeding.

Of course the inevitable car tracker (or average speed cameras) resolve this pretty well.

Other than lost time (which compounds, but also increases traffic congestion, so those 10 mins might turn into 20-25), the fuel use and pollution are greatly increased.

Interestingly, there are speed cameras there, and enforcement is not done on these slight violations: without this flexibility, I'd need to ask for traffic lights to be adjusted so they work well for driving under speed limits, and that is slow and an annoying process.

But without an option to "try", I wouldn't even know this is the case, and I wouldn't even be able to offer this as a suggestion.

Whether that accounts for consequences being "grave and terrible", probably not, but very suboptimal for sure.