There are lots of good reasons not to pollute the earth but staving off an alien invasion designed to disinfect the universe of human pestilence, I feel safe in saying, is not a very high-ranking motivation. Nevertheless, The Guardian on Friday announced that scientists have determined (and reported!) that aliens may want to wipe out humans as a preemptive strike to keep us from bespoiling the rest of space for everyone else.
The shame of that article, other than making the not-ridiculous environmental cause look ridiculous, is that the "report" is a fun paper (pdf); true nerdery worthy of the name (and, by the way, intended for fun, and not actually affiliated with NASA). There are two main questions they try to address: How might Extra Terrestrial Intelligence (ETI) make contact with humans? And in what ways would ETI interaction affect humans (categorized as beneficial, neutral or harmful)?
Have you ever been assigned to write a paper in which the teacher gives only the title or opening line? Give it a try with the title of this paper: Would Contact with Extraterrestrials Benefit or Harm Humanity? A Scenario Analysis. Give yourself a bonus point for each page you write without mentioning Star Trek's United Federation of Planets (these guys barely made it to page 4). See Figure 1 on Page 9 for the cheat sheet on the scenarios they came up with. It's hard not to laugh at the morbidity of the "harmful" list: "ETI eat us... ETI enslave us... ETI attack us..."
There is this though:
Note that the large number of harmful-tohumanity scenarios does not imply that contact with ETI is likely to harm humanity.
Well, that's a relief. :)