You really do not need a ring for a fire. In fact, I do not like rock rings, because eventually your fire sits in a hole and does not get adequate ventilation from below. You simply need to clear a circle of duff and burnable material (like small pine cones, twigs), or preferably start with dirt or sand. Then build your fire. When twigs fall to the side, just push them back into the fire. If you use smaller wood pieces and burn the fire totally, all you have left is a small pile of ashes. There are no soot scarred rocks. Once the ash is totally doused, you could then either scatter the ash or burry them in a hole (like you burry your poop). Then you can "landscape" the site and leave it pretty much with little trace.
If there already is a ring, I use it, but make a vent tunnel. Most established fire pits have too much ash and wood to scatter or burry. I just take a little out as my small part. And pick out others trash if it is there. I do admit that I do not carry out other's glass bottles - just too heavy. Mostly what I find is aluminum foil and food packaging. If I carry a large rock over to sit on, then I carry it back to where I found it.
The same concept should be used when setting up your tent. If you use rocks to tie down the tent, then move them back to where they initially were located. One problem I have with established sites, is that the fire ring is usually too close to the only flat clear spot to set up a tent. It only takes small sparks to put tiny holes in your tent fly, and although the tent fly looks OK you will have small leaks. Same with standing around a fire in your expensive rain jacket. You will get tiny holes from the fire.
I personally hate established campsites. They usually are very dirty. I prefer to set my tent on pristine sand or small gravel. On the other hand, my husband loves established campsites, and to him, the more features (such as benches) the more he likes it. He was a boy scout way back in the 1950's, so I think those features remind him of good times and outdoor ambiance of that age. To him it is an integral part of the outdoor experience. I do not think it is my job to judge his idea of what makes his wilderness experience. By the way, he is an excellent fire-builder. His fires are perfect and burn like a charm. Years ago when we got caught in a freak snowstorm (it generally does not snow that low) on the North Fork of the American River while winter backpacking, and I got soaked, he gallantly built a fire from soaked wood and dried my clothes while I snuggled inside my sleeping bag.
In this whole issue, I agree with what others have said. If it is legal then let it be. Nobody is forcing you to have a campfire - it is your choice. And if you do not like seeing or camping near fire rings, then just go somewhere else.