Like most activities, campfires aren't simply ethical or unethical. There are only a few things in this world that are always ethical or always unethical. Rather, there are ethical and unethical ways to behave. I don't expect a campsite to look exactly like the land around it - I understand there will be artificial clearings in the trees, perhaps a sign indicating it's a campsite, a fire ring, and perhaps a latrine a little way back in the woods. I accept that and in fact prefer that the humans-sleep-here changes to a place are restricted to campsites rather than diffused randomly through the entire natural area. With that in mind, I find it unethical to:
- build a large campfire every day, or several times a day, for no reason other than to cook, when you could use a stove instead
- leave the campsite and surrounding forest a mess
- cut down green trees (which don't burn well) leaving a mess and less live trees than you found
- build complex structures to surround or contain your fire
- make any kind of hole in or damage to a live tree for convenient hanging up of things (I don't even put nails in trees, ever, anywhere.)
I find it not necessarily unethical to:
- gather up some fallen wood (from the campsite and the land nearby) and use it for a small campfire
- sweep the ground around your campfire of tinder and other things that might cause your fire to spread, even though doing so leaves the campsite less "natural" than it was
- use 10 or 20 rocks to build a fire ring
- "furnish" the area around the fire ring with logs, stumps, or rocks for people to sit on
To sit around a small fire in the evening, chasing away the dark with light and heat of our own making, is one of the joys of camping and one of the ways we feel competent and capable. Yes, someone else coming later to my campsite will see soot on the stones of the ring. So? Perhaps yesterday I saw someone's tent, bright blue among the trees, and realized I wasn't actually the only human for a thousand miles. That doesn't make using a tent unethical.
As for overharvesting and devastation, that is best prevented by limiting the numbers of people who use a place, rather than letting everyone in and telling them they can't have campfires. Of the list of troubles campfires supposedly cause:
trampled terrain, delimbed trees, blackened stones, unnecessary trails that weave through the woods but go nowhere, and hatchet/ax scars in trees from 'hanging up' your campfire tools
only "blackened stones" can be laid at my feet, and to be honest a neat fire ring with signs of use and a few logs stacked next to it warms my heart and gives me a sense of connection to those who camped here before me. The rest of it are by no means inevitable consequences of a campfire.