For one thing- you can smell human excrement in parts of Niles Canyon. Its where the homeless camp. Put a path? And you leave the whole canyon open to those who will walk on the flora,tromp ruts where grasses are now, and really make it hard for seedling trees to get started. Throw tree seeds in your kids back yard. See how many trees you get as they tumble and play on them.
This is more of why I hate cyclists. Most are plain assholes,the others pretentious assholes.
If anything, Alameda county should make it HARDER to just walk or bike into the canyon.
I know Environmentalists know this,hell I once did an Earth Day at Niles..what junk we found. With a path? Its nothing but erosion near the creek from now on.
Its not Guadalupe in San Jose..a stream just barely natural with all the "landscaping" and "flood control". I doubt Niles can take any more man made "improvements".