I wish to first clarify that species become extinct naturally all the time. But, I feel this is not the question that was intended.
Each time a species goes extinct due to human activity the entire ecosystem loses. It is a balance that nature manages on her own quite nicely. However, we humans have become more powerful than nature. Our activities, once acceptable, is slowly being realized as not acceptable. Much too slowly. Many more species are becoming extinct than nature can compensate for. I find it inappropriate, and morally distasteful (no offense, just being honest), to think that any one species is less important than the others. They are all important, smart or not, pretty or not, tasty or not.
Peace guys