Driving safely at 70mph is easy. The hard part occurs when something unexpected happens. Most drivers cannot make a split second, evasive high speed maneuver and remain in control their vehicle.
That is why you drive to conditions. On a interstate quality road 70 mph is fine . Unlikely to have pedestrians jump out in front or traffic coming from a side street. In busy neighborhoods you drive to conditions . That doesn't mean flying down at 80 mph on a winding residential neighborhood street.