2. "Slower is better." is a stupid half argument. Speed limits are a tradeoff between the benefits of going fast and the benefits of going slow. If it wasn't a tradeoff then the speed limit would be walking speed everywhere on every road.
2. There are very few benefits to cars going faster. If you want speed, trains are much more efficient at high speed. Fast cars are wasteful and dangerous.
Cars being limited to walking speeds in cities would be great. But failing that, I'm happy with the local groundrule: 30km/h if there's no bike path, 50km/h if there's a raised bike path, and 70km/h if there's a bike path that's separated from the road by at least 1 metre.
Are all these cameras in cities? Are there any on separated highways?