I agree we share some common interests (enjoying our national forests, as you mentioned). There is a point at which politeness doesn't quite cut it at times. My case study is Dutchman's Flat outside of Bend, Oregon. Snowmobilers there are polite and courteous as well, but with the sheer amount of them distributed throughout the area, it becomes a touch intolerable. Yes, one can avoid them after about 5 miles, but those first 5 miles can be a brutal ordeal of smog and constantly checking your back (they have groomed track, but frequently are off it at great speed). I have trouble seeing them as allies at these times.
Anyways, I think both sides of these issues are frequent victims of the commitment heuristic, where we have a desire to be consistent with ethical commitments and decisions we have made in the past. I'm as guilty as the next. Instead of viewing the information objectively and case-by-case we make the same decisions again and again about each other because we want to appear consistent with our beliefs. It makes life's decisions a lot less complex, but it doesn't get us anywhere. Good to see a so-called "liberal" breaking out of it, though I have some fundamental issues with the ARC, of which a great many members are motorized recreationalists (dare I say all?)