Haven't posted to this website since I was in Iraq, but this topic caught my attention.
In the first place, I'm no one's idea of an ultralighter--far from it. I need to throw that out so that what follows makes some sense ("consider the source").
So much for that.
Better writers than I already pointed out that "zero-impact" in reality means "deferred-impact." Kudos for them and they're right. I question the premise that ultralight backpacking can even be seen as "environmentally friendly" compared to other schools of thought. I simply don't believe it can, nor should it try to.
The mantra of "reduce/re-use/recycle," which in my Depression-era grandma's time was "Use it up, wear it out, make it do or do without," applies in my case to backpacking. Most of my gear is, by comparison with yours, ridiculously heavy. It's also made out of a lot of canvas, leather, wool, good steel or brass, and will likely outlast my child's camping career. Much of it is surplus, which means that while there still is an environmental impact from its production, it's diluted over more users. Being surplus, it will last a very long time, and therefore its impact gets diluted further.
The non-surplus stuff--SVEA stove, moosehide mukluks, wool shirts and the like, tend to technology from about a hundred years ago. It's always been my belief that if old-timers could manage, take a look at how they did it and see if the new stuff is truly better (in the case of Thermarests, the answer is of course "yes"). It should come as no surprise that my favorite camping book is CAMPING AND WOODCRAFT by Kephart.
Lastly, the stuff I own is made from lots of canvas/leather/wool, which are renewable. And metal is always recyclable.
This comes at a cost, and not only in weight. Older surplus gear lacks the innovation of newer products and newer philosophies of camping. This is where ultralight backpacking comes in.
Ultralight backpacking focuses more on researching, developing and improving lighter weight ways of doing the exact same thing I do. Research and development of ANYTHING is highly consumptive, period. No getting around it.
The question you as backpackers AND environmentalists have to ask yourself is, is the development of newer, lighter products worth the cost in non-renewable resources. If it is, great. Go forth and multiply, and aside from trying to avoid being flagrantly wasteful, don't give the matter a second thought.
If, however, you believe that environmental concerns outweigh the benefits of developing, manufacturing, transporting, marketing, selling and (ultimately) disposing of a newer lightweight gadget, the answer is likewise simple.
You don't do it.
We should all try to be good stewards of God's Creation, but to think that an industry based on research, development and innovation can pass itself off as "environmentally friendly" and be taken seriously is delusional.