I really loathe places like GSMNP or the Tetons that have designated campsites – but understand why they do it, with the amount of hikers on the trails everyone making their own sites wherever they wanted would be a nightmare for the ecosystem.
If I’m in a situation where I can’t find a site someone has probably used in the past in a Wilderness area or off trail somewhere, I have no hesitation to clear off (remove any surface rocks, tree branches, pinecones, etc) a small footprint for my tent, trying to keep my impact as minimal as possible. In my opinion, if I’m in an area where I can’t find any previously used campsite or anywhere cleared that looks like it could have been used as a campsite, there isn’t enough human traffic for it to make a difference. If it’s an area that sees much use, there are already established sites as people all tend to gravitate to the same sorts of things – flat ground, reasonably close to water, sheltered from bad weather – or have a great view, etc. that sort of funnel people to the same areas.
I’m not saying don’t try to minimize your impact – by all means do, but by clearing pokies, sticks, etc from a small 2′ x 7′ area for your sleeping pad in an area where you can’t find any signs of previous camping, you’re not significantly impacting the area – no more so than an elk, deer, bear, etc bedding down.

