From their website's FAQ, they state, in essence, that we as humans have disrupted Mother Nature's methods of experimentation in developing new biological and ecological tangents.
Mother Nature, as is rather obvious, rewards succesful experiments and exterminates those which are flawed. But, then, why are humans not natural? They address this question in their FAQ as well, and state that we are no longer part of nature as we are a parasitic form of life. (I suppose they ignore the fact that there are many "natural" parasites.)
But wait, as they demonstrate clearly, we have been very effective at changing the planet as we see fit. Entire ecosystems have been eliminated when we take a step. Geographies have been changed because of our fancies. I, for one, see nothing wrong with this.
Biologically speaking, we are very effective. Either species and ecosystems will adapt to us, or we will, directly or indirectly, eliminate them. So long as no truly catastrophic force beyond our control (Nova, Comet) interferes, this tends to be the course of action. Why is this bad? There are many, many species which have gone extinct before we were ever around, and the vast majority went extinct because better alternatives evolved. From VHEMT's own standpoint, one could aruge that we are that better alternative.
Maybe back then things were more green, more pretty, or whatever, but these are subjective analyses. They hold no water. One could just as well argue that we should all go back to any arbitrary epoch of our history because that was subjecitvely better.
To futher usurp this idea of how sacrosanct Earth's ecosphere is one could really turn back the wheels of time and look at Earth when single-celled life was struggling in absolutely horrid conditions to survive. Can we not owe atleast part of Earth's current condition to these early lifeforms? They have disrupted Earth's condition just as we have, they changed Earth to better serve themselves. We have changed Earth to better serve ourselves.
As further evidence to how this is as natural as any other natural processes we can state that we are one of the few species capable of adapting to the majority of changes we inflict on the planet. Say, for example, if Earth were to warm up. The paradigm would change, yes, but we would be far from finished. Any species incapable of adapting to that change would die. Tough. Say things got really nasty and Earth became a second Venus. In the time it would take for that to happen it is entirely reasonable we would have developed a method of survival, either via escaping the planet, transfomring it, or learning to survive under the new conditions. Again, species which cannot adapt to such a change will die. Let's say we really screw up, and we cannot adapt. We will die. A species capable of adapting to our changes will develop. Thus, life, and nature, go on.
"(A+Bn)/n = x, hence God exists, reply!"