Ecosystems also help clean the air we breathe and the water we drink. Without wetlands to purify water and forests to screen out pollutants from the air, we would need machines to provide this service. Biodiversity stabilizes the ecosystem. It keeps our options open for the future. There may be resources out there that we don't yet understand their potentials, and we don't want to destroy them before we even know about them.
Biodiversity also increases the beauty of the planet.
Trying to preserve either a single animal or even the ecosystem are both good ideas if in the long run they work to save the area. When you try to save an individual animal, especially a keystone species , you must provide it with a place to live and food to eat. What better place than its own habitat . Also, in the process of saving an ecosystem, you save all of the other plants and animals in that ecosystem by default. Sometimes it is easier to get people excited about saving an important animal like a parrot or a panda rather than an ecosystem.