From a pedestrian safety perspective, narrower roads and worse infrastructure is a good thing. It slows cars down and makes it less pleasant to drive, so fewer do.

You'd expect so (and I'd hope so) but nope. Drivers become even more reckless. Driving huge, noise-insulated cars seems to put them in the mindset of total control, detachment from actual speed and "I'm not gonna hurt myself anyways". Depending on the country you can add a less than perfect driver education (if any) to the mix.