Not to sound callous, but humans are pretty much the only worthwhile thing in our known universe. Things only have value in the way that they relate to us: a mountain is more impressive than a molehill because the mountain is huge compared to a person. But both are just meaningless piles of atoms without a human observer.
While emotions aren't unique to humans, ours are the most abstract and complicated. We may be the most brutal and destructive species, but we also produced Ghandi and Mother Theresa, and to our credit the average person lies between those two moral extremes.
Most of us would probably agree that torturing a kitten is cruel. On the other hand, a hungry wolf doesn't care about hurting other animals. Nature is just ugly and psychopathic when you really look at it.
This is a dumb question when you think about it. The only way to answer it is to actually be in a situation where you had the ability to kill another human being for no real reason. Otherwise you're just talking out your ass. I'm willing to bet that an overwhelming majority of the people who answered yes would actually puss out if the choice were real.
Nature should be cherished and preserved both for moral reasons and because it is beneficial to human life, but if I had to pick between exterminating humanity or destroying all other life, I would readily let the Earth burn while we flew off in our spaceships to wander the galaxy. And feel sad, of course.
