JJ, horses are not "mechanical transport," that's why they are allowed on trails in some Wilderness Areas.  And every time someone complains about horses in Wilderness Areas, I just shake my head.  Take a look around, if you are worried about a user group losing trail access, that would be horse riders not mountain bikers.  Plus, horse riders are such a small user group.  It is estimated that horseback riders are 10 times smaller than mountain bikers.  Mountain bikers are around 2.8% of the population where horseback riders are around .24% of the population.

And you write "9 times out of 10 this is about a user group (hikers) not wanting to share space, nothing more. It's a "we were here first" thing"   That's totally incorrect.  I'd say the thing hikers want is to hike in peace.  The amount of trails that are hiker only is dwindling every day.   The Forest Service says that mountain bikers can ride on 78% of their trails, that means hikers can only have peace on 22% of the trails.