It is also illegal to stay in the left lane when other people are speeding. If they are going faster than you, you are by definition slower traffic and obliged to keep to the right.
Your job as a driver is not to police other drivers’ behaviors. It’s not even to follow the letter of the law. It’s to operate the vehicle safely. Creating obstacles for other people because you don’t think they should drive so fast is not a safe action.
Really, we need to collectively get rid of the idea of a “fast lane.” The left lane is a passing lane. You should only be in it when you’re attempting to pass someone, and when the pass is complete, you should move over.




Just a quick bit of searching, and I found a Wisconsin sheriff who is far less definitive on this than you:
So Wisconsin does acknowledge that anyone going less than the normal speed of traffic should only use the left lane to pass. But, as the sheriff points out:
And it’s okay that traffic laws conflict with each other because, again, the point is not the letter of the law, but the safe and predictable operation of the vehicle.