I’ll be the first to say that I’m not a fan of mountain bikes shooting down hiking trails. While there are certainly some mountain bikers who are cognizant of others, the vast majority of mountain bikers I’ve encountered have been rude, unsafe cyclists who don’t seem to be in control of their equipment; I’ve seen far more accidents involving bikers running into hikers than the other way around.
That’s not to say that I think mountain biking should be legislated out. I just don’t believe that having a bunch of speeding cyclists who can’t control their machinery sharing the road with hikers is a good thing. Mountain biking is a great outdoor sport, it is great exercise, and it results in some spectacular YouTube footage.