The trails themselves are harmful.

Even hiking has a detrimental impact on fragile habitats.

All human use is burdensome to wilderness areas.

Suggesting otherwise is just a non-starter.

Now, the NFS, NPS, BLM, and so on make a great many mistakes. At the same time, trails do get closed for a reason. I understand that you want to ride your bike on the trails. But the question isn't, what's the most fun for you? It's, what's best for the bears, owls, skunks, and so on, which inhabit that particular bit of land? And it's probably best for them if humans stay out of their faces, especially humans aboard rad machinery. Just a thought.