I think it's more the idea that the speed limit should be reasonably close to what'd be unsafe for long periods, not pressed to the absolute border between what a safe speed and a psychotic speed would be. From that perspective it makes sense that, while you'd ideally like to just go 65 the whole way without obstruction, if you have to pass it's still reasonably to go 67 and do it in a third of the time than clamp to specifically 65 out of ideological principles. If going 67 is just unfathomable from a safety perspective then the problem is probably the speed limit being 65 not what people do to pass at a reasonable rate.