At best, they're a passive aggressive way of exerting government control over citizens. At worst, they're a revenue-increasing mafia-protection-like tool.
If you actually want to protect pedestrians, you build physical "traffic calming" obstacles like speed bumps or chicanes [1]. Switzerland is full of these, and they're very effective. There's really no good reason to have speed cameras (although red light cameras might be a better idea), especially on the motorway (Germany manages without motorway speed limits, so clearly they're not necessary to have a functioning society).
Australia is full of them in sneaky places. It makes the driving experience quite stressful. The speed limits are sometimes ridiculously low and it’s like playing a game.
Speed bumps/breakers are way more effective at slowing cars down. If you don’t slow, you get a big fat jolt and damage your shocks.
I like driving in US much better.
Look at these charts. Speeding rural areas kill! Also, take a guess at what time SUVs became popular in urban areas. https://www.iihs.org/iihs/topics/t/roadway-and-environment/f...