Ecologist Richard Conniff has written an interesting opinion piece addressing the question of whether animals are only important because of their utility to human beings:
As a teacher of ethics, I know full well the temptations involved in appealing to utility to make the case for wildlife preservation. But making the value of wildlife contingent on human needs, I believe is a self-defeating proposition. As Conniff observes, once you start resorting to the issue of utility, you end up getting into debates about what is more important to human beings, and economic development will trump wildlife preservation just about every time.
As far as I'm concerned, the best arguments for the protection of non-human species are aesthetic and moral. Our interactions with animals in the wild--whether we are talking about the bald eagle flying overhead or the rattle snake slithering across our path--is that an appreciation for the majesty of nature in all its forms makes the human soul more beautiful and harmonious. This may sound like an antiquated kind of argument--one that an ancient or Medieval thinker might make--but I think that the argument still holds today.
The philosopher St. Bonaventure once said of St. Francis of Assisi, "In beautiful things, he saw Beauty itself." When one can come to see the divine reality played out in the lives of creatures in the wild, then one will come to see the divine reality in all living things. To the extent that these creatures are viewed simply as means to our own petty human ends, to that extent have we robbed nature of its inherent divinity. And that makes it much easier for us to ignore the threats that are facing animal species around the planet.