by ooli

Finally found it... Didnt remember it was a pdf.

Nick Bostrom webpage: http://www.nickbostrom.com/

Here's the beginning:

But I hope that our Mars probes will discover nothing.  It would be good news if we find Mars to be completely sterile.  Dead rocks and lifeless sands would lift my spirit.    Conversely, if we discovered traces of some simple extinct life form—some bacteria,  some algae—it would be bad news.  If we found fossils of something more advanced,  perhaps something looking like the remnants of a trilobite or even the skeleton of a smal mammal, it would be very bad news.  The more complex the life we found, the more  depressing the news of its existence would be.   Scientifically interesting, certainly, but a  bad omen for the future of the human race.

Great read if, like me, you're obsessed with the Fermi Paradox.

A TL;DR would be like:

-So many planets: Aliens should already been seen, or talk to us. -They did not. So Technological advanced life is rare -If life is abundant (like if we find some on Mars) there must be a "Great Filter" (plague, gamma ray, self destruction, whatever, etc). -This Filter should kill life before it become a galactic civilization. -That's the only explanation for us not seeing any aliens out there. - The only other explanation is : Life is ultra rare. Or the Filter happen early on. -Conclusion: The more advanced are life found on Mars the latter the Filler may occur. -So our Filter still wait for us, and we're doomed.

(A lot of step are subject to discussion. But the pdf is far more clear and explanatory than I could be.)