Other organisms and natural disasters do that, too. Ice ages, meteors, waves of diseases. The difference seems to be we have the consciousness to predict consequences, then decide whether to embark upon a path of behavior, or continue it when latent consequences emerge. I guess the question ends up being whether the course chosen is "natural," and how can we know, since plenty of organisms kill the host, while also surviving and even propagating? Then observation also changes the behavior of things. And we don't kill everything. Just whatever life is left continues to evolve in expected and unexpected ways.