Well two things: we need some of the things in our environment that we also destroy. We need to global temperature to stay below certain levels, but I fucking love flying to nice vacation destinations. My personal interests are in conflict with what is good for humanity.

Also: we need to respect other forms of life. Just like I can't kill someone from another family, even if we are unrelated, it is immoral to kill or damage the environment of another species. I can't kill a human from another family, or other country, without being an asshole. That extends not only to other humans, but also to other forms of life.