Speeding is still illegal, but so is creating a traffic hazard by impeding drivers who wish to speed. The overall principle is that unsafe behavior on the road

Speeding is still illegal, but so is creating a traffic hazard by impeding drivers who wish to speed. The overall principle is that unsafe behavior on the road is prohibited. Full stop. It doesn't matter that your behavior is unsafe only because other people's behavior is also unsafe and prohibited. There's usually a clause in traffic ordinances that state something along the lines of "regardless of any of the other laws here, drivers have a duty to avoid collisions if they can."