If the trail is built in a sustainable fashion, I am all for making a trail unridable (technically) for about 50% of the riding public. Does not mean its always going to be unridable but my favorite trails are the ones where I walked about half of it the first time and after 5-10 tries I am still walking about 10-20% of it. In fact my favorite trails tend to be the trails that only Workman or Phatbiker can ride, and that's about it.
I would sanitize trails only to keep the flow. That means an open and flowing trail I would tend to remove a tree that just kills the mo. If you have a tight and twisty section its best to leave that tree, as its a feature many are looking forward to.
Again, I love tech, I just prefer smartly built. No fall line trails, no shoddy logpiles and nail ridden stunts. If you build a logpile take the time to build it solid, if your going to build a bridge or a skinny*, take some time so that the darn thing don't collapse under the clydedale's weight

(*get permission here, renegade ttf's get us banned)
That all said, some park systems require us, or just come out and remove trees. We don't always agree but they have thier reasons and we can only suggest what we think works. Sometimes they have legitimate concerns that are really not open to debate.