It's not that bad. I ride there 2 or 3 times week all year. I was riding that trail since it was established as a riding trail. It used to be a vague path through the woods. It was a nice loamy path. Then the first school boys race was held and it became a muddy mess. I tried to reroute the entrance to the lower part off Baden Powell as the straight shot was getting erroded. But to no avail. Others would simply move the logs and debris I placed to guide them down the proper entrace.
More racing on those trails brought about more wear and tear and some excellent maintenance.
Now I did ride the trail a few days after the last races and it was indeed well worn and pretty muddy. A few days after though it was drying out and then some horse traffic obviously dislodged a bunch of armouring rocks, like the ones at the large log crossing and generaly churned up the soil and made it a bit lumpy. The exit onto the road was chopped up a lot too. Nothing that little dry weather and minimal work can't fix. I think that the riders won't return because it's a pretty rough trail for horses. The racing probably made the trail noticable to the riders for the first time so they checked it out.
But all trail users have an impact. A trail is by definition and errosional feature. The passage of animals including people over the same patch of ground will create a path through the vegitation down to the soil. That's nature. I have been in the bush hundreds of kilometers from the nearest road and travelled game paths as erroded and worn as the Lynn Loop.
Debate? Bikes are made for riding not pushing.