This idea is rather trendy, and always has been rather trendy, among a certain breed of cynic. Humanity, so the reasoning goes, is an unstoppable force of pure destruction, eradicating nature and exterminating other species wherever it goes. Human beings, according to this line of reasoning, are a violation of the normal natural order; we do not respect the balance and harmony of nature, we spread like a disease and corrupt everything we touch.
Bullshit on the harmony and balance of nature; there is no such thing. Bullshit on the natural order; competition and destruction are writ large into it. Bullshit on the entire lot of it.
Now, it is true that humanity can and often is destructive to other species. Countless thousands of species of life on Earth have been rendered extinct through the direct or indirect action of man. This loss of species, and the attendant ecological damage that goes with it, is an appalling waste that can not and should not be justified. So clearly, the world would be better off without us, yes?
No. As appalling and wasteful as it is, if you take man out of the equation, nothing changes. Widescale, rampant species extinction is a part of natural history, and man, for all his inventive, monkey-brained destructiveness, isn't even terribly good at it.
Remember all that stuff you've heard about the balance of nature? It's bunk. There is no such thing. "Balance" occurs in nature only when competing species fight one another to a stalemate. The stalemate never lasts; as soon as one species gains the upper hand, it's curtains for the loser. Nature is not about balance and harmony; nature is a ceaseless war, with no quarter given and no mercy granted, and the loser is wiped out, never to return. This has always been the way of nature, since long before man with his high cranial capacity and penchant for language and tool-use, arrived on the scene, and it will continue to be the way of nature if we all disappear tomorrow. The way nature works is pretty straightforward: get resources, at the expense of every competitor and by any means possible, or die.
Our big brains--those ones that give us language and reason and analytical cognition and spears and flint knives and bulldozers and iPods--are tools of survival, just like fangs and claws. We use them to do what every species uses its tools for; we use them to survive.
There's an interesting thing about those who want to end the human experiment; they don't apply the same values to the rest of nature that they do to humanity. If a predator like a lion hunts some prey animal into extinction, they don't see this as a tragedy. If a new species arises that entirely dominates its ecological niche, displacing and then destroying all its competition, they don't call for that species to be exterminated. Only humans get judged that way.
And if you say "That's because only humans know better," you've just made my next point for me.
Humans are hardly the most destructive species ever to rise on Mother Earth. That honor would have to go to the lowly cyanobacterium, the first photosynthetic organism and in terms of raw biomass arguably the most successful organism on Earth. Yes, I'm talking about plain old ordinary blue-green algae.
You see, when life first arose on Planet Earth, there was no oxygen in the air. This planet, like all rocky planets reasonably close in to their star, began with a reducing atmosphere, not an oxygenating atmosphere.
Life evolved here in a reducing atmosphere; and to an organism whose metabolism is not based on oxygen, oxygen is a deadly poison. The problem with anaerobic life, though, is that it tends to be rather sluggish. Metabolisms not based on oxygen aren't very energetic; oxygen is a boon, because it allows for a very fast, high-energy metabolism, but it's also a curse, because it's corrosive and toxic and tends to degrade and destroy complex organic molecules.
Life got along quite splendidly without oxygen, until the arrival of blue-green algae and a newfangled survival tool called "photosynthesis."
Photosynthesis is a complex and fiddly process, which is why it took a very long time for any organism to make it work. When it works, it works well, though, because all you need to power your cells is carbon dioxide, sunlight, and a few other trace elements. But it releases oxygen, and oxygen is bad news.
For everyone else.
The arrival of photosynthetic cyanobacteria forever altered the planet's atmosphere. Cyanobacteria spread like wildfire, because they had a great schtick: they could produce energy from sunlight, and the metabolic byproduct--oxygen--poisoned everything around them, wiping out their competition and providing fertilizer at the same time.
If you weren't a cyanobacterium, it was a disaster. Species were exterminated everywhere the cyanobacteria went. As the atmosphere changed, species were exterminated everywhere, period. Only two species of life are known to have survived the catastrophe--one of them a type of anaerobic bacterium that can sometimes infect people, and the other a pesky anaerobic bacterium that causes botulism. Everything else? Gone. Destroyed. All wiped out--down to every species on the whole planet save two--by blue-green algae.
A commendable accomplishment, if one values this sort of thing. Certainly an accomplishment man has yet to equal.
Now, nobody I know of has ever called for an end to the "photosynthetic experiment," nor said that oxygen-producing life is a disease on the planet that must be eradicated. You see, when blue-green algae causes an ecological catastrophe on a global scale, wiping out countless species, it's all part of the natural order of things. Yet when man does the same thing, we're a blight on the planet. The difference? We know better.
And that illustrates a very important point.
The idea that species should be preserved? The idea that extinction is bad? The idea that natural living things have value in and of themselves? These are human values. They are not found in nature. Only human beings hold these values. These values are only meaningful to human beings. Humans are alone among all forms of life in the sense that we alone can form abstract ideas about good and bad, we alone can see and appreciate the value of things beyond their value as food or competition.
Nature is a bitch. Nature is fine with mass extinction. Nature is fine with smacking an asteroid the size of Boston into an inhabited planet, killing every land animal with a body mass over five kilograms or so. Nature is ruthless, uncaring, and indifferent to whether something lives or dies. To nature, a planet teeming with life is just as good as a sterile bolder; it's all the same. Ideas about whether or not something "deserves" to live are not natural; these ideas exist only as human ideas. And that makes all the difference.
The person who wants to pull the plug on the human experiment does not realize that doing so would not actually accomplish anything. It would not create order or harmony; it would not stop the endless cycle of competitoin and extinction. All it would do is destroy something unique, something which has never in the history of this world been seen before.
It would remove the one species of life on this planet that has the power and the ability to destroy another species, and can choose not to.
Humans are not unique in their ability to upset ecological systems and destroy other species. It's pure hubris to believe that we are. Indeed, it's arrogant to believe that we could destroy all life on earth; even our entire nuclear arsenals would likely not be able to do this. Destroying all life on earth, down to the last bacterium, is a more challenging problem than it seems. The cyanobacteria came pretty damn close, but there are nontrivial problems like deep-sea volcanic-vent organisms, bacteria that can withstand enormous doses of radiation and form spores capable of surviving for thousands of years, and pesky things like that which would quite likely thumb their noses at any attempt on our part to wipe out all life on earth.
But we are unique nonetheless. Our uniqueness lies in the fact that of all forms of life this planet has ever seen, only one has ever chosen not to compete with another species--indeed, even chosen to support another species, and sought to preserve it--when there is no direct and immediate gain in doing so. We as a species do know better; and the fact that we are capable of holding values which say that extinction is bad, and are capable of acting on those values, and indeed are even capable of saying that we should eliminate ourselves in order to protect competing species (species which, it must be said, would have no similar qualms about driving us to extinction were our roles reversed), is proof that we are not merely an unchecked destructive force.
We alone among all the billions of organisms which exist or have ever existed on this planet can form value judgments about the consequences of our actions. We alone among all the organisms which exist can see the beauty in other life simply for its own sake, and choose not to use the tools nature provided with to survive at their expense. We alone can say "I have the ability to use my big brain to out-compete this species, and I see gain in doing so, but I will not."
A predator that drives its prey into extinction soon follows; and in fact this happens all the time. I'm not suggesting that protecting other life is entirely altruistic; the same can happen to us. But that, too, makes us unique; other species do not see the consequences of their struggle to survive, and we do.
The law of nature is "survival at all costs." Only human beings, alone of all species, can say "this cost is too high; I choose another way."