Okay, I'll be a dissenter here. what's wrong with a little blowdown, it leaves "a little" charm and variation to a hike. Climbing over or ducking under occasional trees sometimes can add a little fun to an otherwise BORING trail section. MANY (not all, but many) trails are so well maintained, they might as well be friggin paved.
I personally don't see a huge ethical violation if a hiker "feels compelled" to move/cut/destroy/annihilate every forlorn little branch or tree that happens to fall in the path, but I also don't see a huge need for it either. An obvious exception would be huge deadfall, that creates a physical hazard or is such an impediment that it causes other to create "new" work around trails, which is BAD.
For the most part though, I consider it part of the adventure to negotiate natural obstacles along the trail. On maintained trails, it obvious, someone needs to go in every year to keep the path free of major obstructions, but I don't see a huge need for someone to be out there whacking away at every branch the second it hits the ground.
Look at it like this, like many, I mumbled, grumbled and swore my way through the herd paths to Cliff and Couch (ADK's) while doing em', but ya know what, you gotta admit, those paths/peaks have some serious character (personality even). The VanHo route up Marcy (to the treeline anyway), has about as much character as I-87 for me.
That's just my opinion. btw, this is for trails only, I strongly feel that if you decide to color "outside the lines", you need to leave the permanent markers at home