I am a long distance walker. I live at the top of a hill on the outskirts of Conwy. The road up the hill has no pavements and is within the 20mph speed limit. I walk down (and later) up that hill most days and from there on to Llandudno or the Supermarkets or to the bird sanctuary. Other people walk up and down that hill walking their dogs, or posting a letter, to catch the bus, or to get from the caravan sites into town.
When the limit was 30 mph only a small number of cars stuck to that limit on the hill, the others wizzed past me sometimes with inches to spare due to a car approaching in the other direction. Now with the 20mph limit I feel even more vulnerable. I am guessing that the same drivers are ignoring the limit and are approaching the hill frustrated by being held up earlier by cars sticking to the limit and are driving even faster and more aggressively up the hill.
Many of the roads on my walks have pavements on both sides making the roads perfectly safe to drive at 30mph along. If only consideration had been given to which roads were dangerous and the 20mph limit applied to them I think we may have benefitted from it. Applying it to all roads has just resulted in frustrated drivers who are a danger to pedestrians.