You're talking about a system where one kid running into the road could cause a chain collision of dozens of cars that were counting on rushing the intersection at high speed. Or, alternatively, could end up with the kid getting hit at 45 miles an hour, with extremely fatal and destructive results.
Maybe the car detects the kid earlier. But that's not guaranteed; if the kid runs out from between two parked cars, for example, there may not be sufficient time at higher speeds for the car to stop.
People behave unpredictably. Hell, even when they behave predictably and cross at the crosswalk when they’re supposed to, they can still get hit by cars.
That said, on-street parking does have the benefit of placing a multi-ton shield between traffic and pedestrians and cyclists. Slower speeds and better street design can at least lessen the likelihood of fatal accidents when people pop out between parked cars.
Slower speeds work for sure, but getting a robo taxi to adhere to those slower speeds is much more realistic than getting a human driver to do the same.
The answer is to take that into account with traffic calming measures[0] that alter the street design and make it more stressful for drivers. Narrower lanes, big trees overhanging the street, small traffic circles, pinchpoints, and other measures making driving fast very uncomfortable. You feel like you need to pay more attention, and drivers naturally slow down as a result.
0. https://globaldesigningcities.org/publication/global-street-...