I think that horses have been "grandfathered in" to the park, in respects to trail rights, because of their initial help in the construction of trails and bridges, or so I have been told.
I agree that they damage trails, streams, & campsites, although I won't place any additional blame on them for trash being left in the woods, as I have been extremely disappointed at the amount of trash i've seen on foot traffic only trails lately.
I'm sorry that Rainbows were found, again, in Lynn Camp. Thanks to everyone who has done work throughout the years in an effort to restore our native fish species. Hopefully everything will work out as planned in the end.