True, but gently slowing down on a residential street near a school feels unlikely to lead to other drivers attempting high speed tailgating, undertaking or other aggressive manoeuvres that might result from, say, hogging the overtaking lane without actually overtaking because you're sticking to the speed limit, even before the obvious downsides of speeding near schools are considered...

(Also, the second case is something a car manufacturer should probably be resolving more by not hogging the overtaking lane than defaulting to going 20mph over the limit for extended periods because everybody else does)