Their site is pretty damn funny though I'd say its 50/50 ratio of real to bs. A lot of their info on erosion damage, soil compaction, and water pollution is correct. My favorite is their bias against snowmobiles. I've ridden snowmobiles since I was 8 and I've seen more deer along the trails than I ever have hunting. Their usage of the term "noise pollution" is like "light pollution". The word pollution is defined as "the introduction of harmful substances or products into the environment" and noise is not applicable to that category. I'm unaware where they got the information about snowmobiles dumping that amount of gas out the tail pipe or jetskis doing the same thing. If it does infact do that its not a good thing but not the worst. Gas will evaporate pretty damn quick from a lake or ocean its a little harder if it hits the water table.
The soil damage is a concern the US Environmental Protection Agency (EPA) takes seriously. They do not like rutting of any kind, damage to protected or endangered plant species, or disruption of wetlands. So I would recommend having established a club for offroading like snowmobilers have set up in their states.
I'm gonna keep looking at their website and try and pick out some of the bs. But it still basically boils down to having the public on your side.