I have to say its obvious in this thread those who have not dealt with horses
A horse is not just a big dog. They act completely different to stimuli.
A horse is 1000 pounds+ No matter how hard your dog pulls there is no comparison.
A dog can't kick you and shatter bones.
A dog (likely) comes back when you call if the leash is jerked out of your hands.
Your dog isn't likely wearing thousands upon thousands of dollars of equipment (that can get destroyed if running loose)
Your dog is not in any way physically harmed by you picking up poop. (mounting and dismounting IS hard on horses)
People can pass you on the trail if you are stooping and scooping, not likely with a horse.
You can just use your hand and little bag to pick up the poop of your dog. What pray tell would you suggest a rider use?
Your dog stops to poop, its easy to tell they are pooping. Riders have mentioned that yes it can be impossible to tell that your horse just went.
Dog poop is gross, slimy, sticky and pungent (at least for non raw fed dogs) horse poop is firm, non sticky and made of grass/
Dogs are companion animals, horses are still legally forms of transport. Do you clean up bits of oil your car may leave in parking lots? (just wondering.. as that is actually harmful)
Its simple to poop and scoop even with an under socialized under trained dog.. even with a bomb proof horse its not going to be a simple 20 second activity.
People with minor mobility issues can still poop and scoop for their dogs, will they be able to get on their horse repeatedly from the ground (forgetting its harmful for the horse)
I too have had horse's fall on me.. its not fun.
So horse people have pointed out its going to hurt horses (physically, no matter how well trained) its going to add danger to horses, people, and equipment.
Horse ARE far more dangerous than dogs... here are some statistics for you non horse people...
Horses are the most dangerous domestic animal (NEISS 2001-2003)
for ever million horses there are 10,000 injuries treated in emergency rooms.. compared to 1/2 that of dogs.
There are 2.16 human fatalities per million horses per year. Dogs don't even come close to that number (I think it was .3 human fatalities per million per year.. its hard to read the chart as its so low)
Horses are dangerous animals, there is no getting around that. I have lost friends to riding accidents. I have been kicked, fallen on, tossed, nerve damage, broken bones etc myself. (I worked with a lot of 'problem horses'.. but a lot of those injuries came from well trained horses when something flukey happened)
So far all you people who think horses should be allowed on the trail but should have no issues picking up after them selves... well I suggest you go take some riding lessons or spend some time working with horses... then we will talk.