I think trail damage from riders is alot less damaging than from hikers. Some of the most pristine trails I've ever ridden had probably never had a foot set on them for the most part. With hikers and walkers comes trash, erosion, and people leaving the trail. Mountain bikers tend to be much more environment concious because they realize that if they don't take care of their trails they may no longer exist! A single narrow path that is no more than a foot wide running through a pine forest is going to do little if anything to the environment. Foot traffic however brings lots of trash, and garbage too. I don't buy any of that crap. A 2 inch tire to me would have less impact than a foot will.