Why would that ever be a goal?
Spoiler Alert!
In the late 21st century, Earth is at peace, sending fleets of Valerie spacecraft to the stars. Without warning, relativistic kill vehicle obliterate the surface of every planet, and a mop-up fleet of ships begins hunting down the humans that remain.
The last two humans on Earth are kept as zoo specimens. They ask why their planet, and all its species, were exterminated. The squid-like aliens explain their logic thusly:
1. Every space-faring civilization is capable of planetary extermination.
2. If given the choice, every species will choose to exterminate another species rather than their own.
3. Each side knows that the other has the same choice.
As much as his ideas and methods were bonkers and would never work the fact that humans have stopped evolving naturally is something that some people still want to change.
More information: http://en.wikipedia.org/wiki/The_Holocaust#Development_and_e...
PS: Humans closet genetic relative is a single celled organism whose species started from cultures of a woman's cancer cells. http://en.wikipedia.org/wiki/HeLa Tasmanian devils suffer from a similar disease of more natural oragin. http://animals.nationalgeographic.com/animals/mammals/tasman...
The obvious plan is glass the planet, spend 50 years harvesting the orbital resources and then you'll have the infrastructure in place to strip mine the lifeless planet.