Extinction is often thought of as a specifically negative thing. The loss of any group of animals or biological organisms is seen as the permanent removal of that unique species or strain, and since genetic technologies have not progressed to the point where those organisms can be reproduced, any future benefit of their genetic material -- such as unique hormones -- is lost as well. Extinction events can also predict or herald a major change in the worldwide ecosphere, with the possibility of affecting many other organisms.
However, there can be positives to extinction as well. While the extinction of larger animals and birds can affect the ecosystem -- for example, the loss of a predator can cause the prey population to expand, possibly harming plant life in the area -- the loss of microorganisms does not have as much of an impact, and can be extremely positive overall. The most famous example of a positive extinction is the smallpox virus, which until the development of an adequate vaccine, was extremely contagious and deadly. Vaccination programs caused the virus to generally die out in the world; today, there are no naturally-occurring cases of smallpox, and millions of lives have been saved as a result. This is an example of a deliberate extinction event. Interestingly, some current research finds that the smallpox virus might help battle spreading cancer cells.
Extinction is part of entropy and evolution, which dictate that all systems move towards general equilibrium over time. As such, it can be seen as a natural law; most animals and plants are destined to become extinct, and will be replaced by new genetic strains. Deliberate extinction events must be examined closely before they are implemented, and care must be taken to preserve the current state of equilibrium that exists in many parts of the world.