You're right, Martin - it's the amount of traffic as much as the type of transport - whether Shank's Pony or 4x4... I think most of us could agree that the rants now seem to be about inconsiderate or just plain ignorant people - not the transport they choose! I have met very ignorant horse riders when on foot, and it wasn't the horse's fault.
I agree most mountain bikers use specific forestry areas for their sport, but the occasional one escapes into the hills. All I can suggest for them is to ensure their little bells are aerodynamically shaped. If it goes in easy, it may come out easy too....
Haw haw haw!