Is this rule above the other rules like speed limits, stooping at red light ? It seems to me that this kind of fuzzy rules can undermine the others.

They both can apply. The flow of traffic laws, such as the one in California, are to prevent people from going significantly below the speed limit. Its a better approach, in my opinion, then a minimum speed limit law that many states use.

That said, you'll end up driving white-knuckled and fearful of your life if you dare go the speed limit on the Mass Pike. You'd have to drive 70-75 minimum here just to feel safe.

Yes, it makes sense for the minimum speed, here in Europe the max speed can't be exceeded and on top of that you have to adapt your speed to the actual condition, if is ice or the road is wet, or there is fog the law says you have to reduce your speed until you are safe, if you did not reduced it enough and did an accident you are guilty.

I hate when someone drivers respecting the limit and you get jerks with big cars or trucks behind you and force you to go faster(by force I mean get close behind you, use the horn and other bad behavior that can intimidate a new driver).

At least they are not firing missiles.