You don't know that traffic won't flow well at 100 km/h, because traffic never flows at that speed unless forced to by an obstruction ahead. I have been in heavily enforced areas of New York State where interstate traffic flows well at around 110 km/h, including the occasional out-of-state RV doing 90 km/h.
We have no lane discipline because it's not the law. You must keep right when going slower than the flow of traffic, but there's nothing I know of to keep you from going with the "flow" of 120 km/h in the left lane, while someone else behind you wants to pass. As long as you keep them from passing you, you're not breaking the law that states you much turn to the right when overtaken. 'Unnecessary slow driving' doesn't seem like it would apply, either, because you're going with the flow.
Also, speed limits don't always have to be about safety. Drag on a car increases dramatically as you go above 100 km/h. Lots of gas to be saved by having everyone drive slower. If you need to get to your destination at the speed of sound, then you might want to reorganise your life.
And no, I'm not a goddamn hippy. I vote Conservative and support the death penalty, goddammit!