Conservation is absolutely futile. Unless we get a grip on overpopulation
No doubt. But overpopulation and environmental destruction both stem from the same basic problem, which Guitarhacker has eloquently expressed in his metaphor about his guitar, " I don't care if it was made from the last mahogany tree on the planet." The problem is not that there are too many of us (although there are) but that there are too many of us who do not care about anything except what we personally want to own. The massive deforestation of the North American continent in the last three hundred years is just a large scale application of the primitive slash and burn mentality that brought humans out of the caves.
In sparsely populated regions of the planet, the few people available still tend to exploit the resources as aggressively as their (in some cases primitive) technology will allow. The myth of the spiritually superior noble savage who only hunted what he and his family could eat, was given the lie by the introduction of snowmobiles and high powered rifles. Given the option to hunt their prey to extinction and sell anything they could not eat themselves, members of "traditional cultures" have become among the most destructive of our species. We were just as destructive in our hearts when our numbers were small, and our powers were weak. Now we are many and powerful and just as short-sighted and greedy as we were when we first took up tools.
The desire to make many children in spite of the limit to the planet's ability to support them is not so different from the desire to cure our impotence with rhinocerous horn, or cut the last mahogany tree to make a guitar. What I do find interesting, however is the overlap between people who demand that we stop collecting taxes to help our neighbors, because doing so will burden our childre with crushing debt, and those who find no problem following a destructively selfish course of action that will leave those children with a barren planet.
So yes, I agree that conservation will eventually fail. The greed and lack of compassion and imagination that is our behavioral heritage as a species acts as a constant ratchet that locks every destructive action against the possibilty of backsliding into preserving what we cannot create, or even just letting it be. Still knowing that we will all die does not mean we should accept murder.