Honestly, I've been mostly talking out of my ass about that one. It's just sad to see all the rocks gone. Does anyone build trails with rock gardens anymore? When I'm joining trail building parties with the local NEMBA guys, rocks are almost always being removed for the trails to be easier, even from previously well established trails...
I stopped supporting my local MTB club because of this. I used to get into pretty heated arguments with folks during trailwork because of Rock/Root removal. The worst part is that most of the stuff being removed wasn't even technically difficult, they just wanted smoother trails. Of course when it rains here it comes in downpours, so those trails are now all eroded, because rocks and roots hold shit together.
When I lived in Cleveland, it seemed that people would search long and far for rocks, then put them in the middle of the trails. Different scene out there, much more of a blue collar activity, not full of the dentists/lawyers we have here.