I disagree, idiots are everywhere.

The thing is, the vast majority of people - regardless of culture - have some basic sense of self-preservation. Speeding is easy when that 30km/h road is designed like a 120km/h highway. Speeding is a lot harder when that 30km/h road has speed bumps, chicanes, bottlenecks, and is paved with bricks rather than asphalt: if you try to speed, it'll quickly feel like you need to be a professional rally driver to keep your car under control.

Deliberately making roads "unsafe" forces people to slow down, which in turn actually makes it safe.