Why should we care about the environment?

Too simple question? But it is the question that have haunted me since 1997. What do you think? Why do we have to care? Quick response may be, "The environmental quality degrades badly, and it could endanger human existence in the future. So, we have to do something now for the future generation." Then let me ask, "Does the environmental quality get really worse? You may say about global warming, but is there enough evidence that global warming means total extinction of human species?" As everything has two aspects: good and bad, global warming may have benefits and costs. For example, in temperate zone, now large tropical fish are often caught. Fishermen can benefit from the new species. Of course, there is a issue of resilience and adaptability of human economies to the new change, but I cannot accept the idea that global warming has only dire scenes. There must be some opportunities coming with it. What are the real benefits and costs from the environmental protection? Do we need conserve the environment as pristine as it was? I have been lived as an environmentalist for 10 years. Now, I want to see the truth through the cloud of ideologies.