I get very tired of hearing this kind of argument. Generally, those who put it forward forget that mankind is a part of nature. ALL life does harm in some way or another. Nature has ways of balancing things out. If a group grows beyond the capacity of its food source the weaker members of the group die off. the group gets smaller until there is once again enough food for the group. Mankind is no different, except that: #1, we eat virtually everything, not just one particular food; and #2, we have devised ways to increase our food supply to match our population growth. At least so far. It's a zero sum game, though. Eventually there won't be enough to go around. Then the weaker individuals, families, tribes, populations, will die off, reducing the demand.
This is the key thing to remember. We are not destroying the earth, we are destroying the parts of the earth where we live. We are making it less habitable for ourselves. Just as I noted above, eventually the population will decline, through famine, war, disease, those "natural" processes which have been with us for millennia. Understandably, no one wants to be part of that decline, but those who live through it will find a much different world than we live in now. Just as our world is much different from the world of the Neanderthals. Will it be better? Who knows? It WILL be different, though. That's guaranteed.btw - by destroy the world I meant destroy it for mankind. The world will recover after we've all gone, with just a thin layer of oily (or radioactive) material separating one era from the next.
I'm reminded of a comment by George Carlin (I think): Perhaps mankind was Nature's way of getting Styrofoam. Now that she's got it she doesn't need us anymore.