As with most, though not all, issues I think it's wrong to make blanket statements about building fires.
It seems that the consensus, with some opposition, is that minimal-impact stoves such as the Bushbuddy or a Kelly Kettle (aka Benghazi Boiler) are acceptable alternatives. I certainly think so. Since they burn twigs and leaf litter I think they are materially different than a campfire buring larger deadfall, especially since most of the people that use such systems are those of us who are far away from the busier trails.
Nonetheless, I have to support the burn bans in national parks, since there are simply too many irresponsible people infesting the national parks. BLM land and national forests are another matter, though. Few Joe Sixpacks like camping in real wilderness. My friends and I had campfies every night when we were kayaking through the Tongass this past summer. Not bonfires, mind you, but little camp fires.
One of those rare absolutisms:
Anyone who says that burning wood is no more carbon neutral than burning propane needs to do a little reading. The carbon in fossil fuels has been locked underground for at least 50 million years. It is unlikely that the Earth was cold enough to have ice at both poles at any time before 65 million years ago. Here's a source:
It is the difference between freeing carbon that is currently participating in the carbon cycle (wood) versus carbon that has been out of the cycle a long time (fossil fuels). Before that carbon was taken out of the cycle the Earth WAS exactly what all the global warning fanatics keep screaming about, or worse. So if you want another "Hothouse Earth", by all means, burn those fossil fuels and increase the atmospheric CO2 by 500%.
Alcohol is NOT carbon neutral. All the studies show almost no improvement over fossil fuels, because it takes so much fossil fuels to grow the source vegetation (fertilizer, tractor fuel, seed trucks, etc.), move it to the processing center, move the alcohol to the stores where you buy it, etc.
That said, eventually we may get to the point where it isn't a bad choice. We can learn a lot about how to do it from Brazil. Right now, speaking purely environmentally, alcohol is essentially just as bad as fossil fuels. But then again, what is one propane cannister compared to the gas you burned getting to the trail-head? A drop in the ocean, that's what. There is no truly good option. We have to accept that humans are going to affect the planet, and just try to minimize it. We can't stop it at this point; there are too many of us (and growing). Thank you, Malthus.