I have a problem with this statement! Why is every person who rides and ATV labeled a fat slob? Why is it OK for someone to ride a horse compared to someone riding an ATV? They are both riding something that is making it easier on themselves. I wonder how many "horsemen" would walk that canyon on their own two feet.
I have nothing against either group. I have ATV's that I use responsibly and I have used horses plenty of times. Honestly I feel as lazy riding either.
I have seen people on horses gathering shed antlers in a motorized restricted area chasing the bulls trying to get them to drop an antler. (Yes I did turn them in)
In my opinion if there is any kind of travel restriction then it should be for everything except people on foot.
It comes down to impact. ATV's have a much greater impact on the resource than horses. Horses have a greater impact than feet. The ATV crowd has largely earned their reputation through their acts. Does that mean everyone on an ATV is a law breaking jackwagon? Of course not. But it does mean that impacts by those who have ignored restrictions and regulations ruin it for everyone.
That's how life works.