Alright, here it is so that people with no critical thinking skills can get it:

Nobody, at any point, said we should make the speed limit on all roads 6 km/h.

Nobody even said we should make the speed limit on some roads 6 km/h.

The actual thing actually proposed by road safety advocates and people in favour of better urban planning is reducing the speed limit on local residential streets, and in commercial shopping districts. Usually to 30 km/h.