People have an effect on the planet, period. So do birds, cows, fish, microscopic organisms, etc. The real debate should be about what cockroaches we humans really are. We are basically using up everything around us in the hopes that we can move on one day to another place, or just manufacture substitutes.
Will we kill the Earth? Now that's just absurd! Unless we buried all of the nuclear weapons in existence in one spot and hit the button, we can only have an impact on how livable the planet is for organisms with certain needs such as specific amounts of oxygen, sunlight, etc. Of course, as these organisms die due to the change in environment, others will begin to adapt and prosper. Natural cycle.
This doesn't mean that I don't recycle, reduce as much waste as I can, and try to drive low emission, high MPG autos in an attempt to minimize my personal impact and to enjoy the state of nature as much as I can. I just think the idea that the human race is destined to be around for any appreciable timeline compared to the Earth's existence is folly.
Long after we are gone, a mere fossilized record of a species that once ruled the planet, Earth will have incorporated everything we have produced into another version of itself, complete with plastic rocks, Styrofoam trees, and radioactive grass, but why worry? We won't be here anyway, but I bet the cockroaches will have high-fi by then.
