I grew up around horses and enjoy their personalities, but dislike slogging thru horseshit on the trails. I've never met a hiker who told me how much they enjoy meeting horses on the trails, either. Certain groups just don't mix well - hikers and snowmobilers don't mix well. Neither do hikers and horses.
Horses aren't native to the Sierra, at least since about the Pleistecene era, if memory serves. They were introduced by Europeans. As for their work in support of backcountry trail maintenance - I can't speak to that. What I do know is that trails I sometimes hike, including parts of the PCT, get rather chewed up by horse traffic and free range cattle. Personally, I've never seen anyone on horseback doing trail maintenance on the PCT, but perhaps they do.
If horses are needed for essential services in the backcountry, then I'd like to see pack animals considered who have less impact on the environment. Llamas come immediately to mind. I've watched them pack in/pack out organic matter from the high elevation toilets near Longs Peak, and am amazed at their speed, agility, and minimal impact on the treadway. Plus, their droppings are dry, like goats, sheep and rabbits.
I'm not persuaded that there's a need to continue to use horses for purely recreational purposes in the backcountry, particularly in designated wilderness areas. We no longer allow motorized/mechanized vehicles in the backcountry, maybe it's time to phase out horses for recreational purposes. Not immediately, but overtime - perhaps 5-10 years.
