hmmm, do off road cars do any damage? How about tanks, bombs, airplane accidents and acid rain? You think a glacier from an ice age ever knocked over an 'ancient and rare rock formation'? Or a meteorite? A tornado? I don't think the biker adds his fair share of destruction but that's just MHO.

What you didn't see is the next MTBiker come flying down the hill and crashing directly into the 'ancient and rare rock formation' and knocking it over.