Have you ever driven through a downtown urban area? You can't go more than 30mph anyway, even if you wanted to. There is simply too much connections, turns, etc.
And yet, I still disagree that pedestrians should be able to just enter the road willy-nilly. Crosswalks are there for safety because it sets the same expectations for everyone using the road, drivers included, thus creating order and flow that is generally reliable.
This is also the same problem I have with cyclists that think they should be allowed to ride against traffic, ignore stop signs, etc. By not moving with the expected flow, they endanger themselves and creat problems. When I am making a right hand turn, for example, and a cyclist has decided to ride against traffic, I am not compelled to look to my right as I am timing my turn because I am not expecting traffic to be there since a right turn has you crossing zero lanes of traffic and merging with on-coning that would be on your left.
I don't really like our car-centric roads in the US at all, but rules are in place for a reason.