Driving the speed limit is far safer than everyone just making up their own speed limit and driving as fast as they "feel."
Don't like the speed limit? Press the lawmaking authority in your community to change it.
I never said "everyone driving the 'safe' speed limit would create a traffic panacea," but it would be safer than some driving the speed limit and others exceeding the speed limit by 10 - 30 mph.
The video at the link provided directly contradicts that claim with real-world evidence.