I'm sure I'll get flamed for this, but to me, the issue with the bill is proof.  Prove beyond a reasonable doubt that either you were in danger, or some other outstanding circumstance caused you to hit the protester(s).

The only instance I can think of where I'd say the driver was not at fault was a video I saw where protesters filtered out onto the highway when it was dark outside.  They used their flashlights on their cell phones to try and light up the roadway.  Sure, at 10 feet, those flashlights are pretty bright.  But according to http://www.government-fleet.com/content/driver-care-know-your-stopping-distance.aspx, at 70mph, the distance traveled between the time you realize you need to slam the brakes on, and where you stop, is about 350 feet.  Gather up 10 friends, go outside tonight, turn your phone flashlights on and see what that looks like 350 feet away.  In that specific scenario, there's no way a car would be able to stop once it realized that people were on the highway.