Maybe, but the horse riders have boatloads of money (In my experience), attend meetings, and have historical precedent on their side. Mountain biking is still new.

Horse riders can always look back to a time when what they now do for sport used to be the only form of transit.

I come from a family of horse riders, and am a mountain biker. Really, it is completely possible to get along and share the trails. Obviously, some trails are only going to work for mountain bikes, and some are much nicer for horses (and boring for bikers).

I'd love to see horse riders required to clean up after their horses, just like dog owners clean up after their dogs. It's your pet, clean up.

Horse shit is mostly grass and other plants and doesn't really smell much. It will rain away or compost to dirt much quicker than smelly dog poop. But yeah, might be an idea to shuffle it out of the trail.

It's still shit. When I have to avoid it while biking or walking, it interrupts the tranquility of my enjoying the trail.

On a more serious note, a major problem with animal feces on trails that are shared with bikers is the risk it poses when you run it over, and it splatters all over the place. If it gets in your mouth, or on the nozzle of your water bottle or camelback, you can get sick.

The horseshit is awful on the trail up Half Dome. It may not smell that bad to someone who loves horses, but I assure you it smells to someone who doesn't.

In may be purely aesthetic, with no basis, but as a hiker I hate sharing a trail with cyclists. In a weird unsubstantiated way, I feel like horses are like other hikers. I've never had a horse like, gallop by me on a trial.

This is the number one reason why I hate sharing trails with cyclists. I've never seen a horse going over 6MPH, which is a light jogging speed, and they tend to go even slower downhill. Set a universal speed limit of 10mph on the trail at all times, which is a reasonable upper limit for horses and trail runners, and I don't think you'd see many cyclists.