The cited paper describes the hypothesis of “The Great Filter,” a
proposed explanation to Fermi’s Paradox, and the explanation I find the
most compelling. According to a hypothesis there is a Filter causing
potential civilizations to never attain interstellar colonization, but
where exactly this Filter lies is unknown.
If the Filter lies past us, if say, the Filter is the chance for life to originate then we’ve long
since past the Filter and have nothing to worry about, but if life is
common in the universe (this is the reason why some scientists dread
discovering alien life on Mars and Europa) then we haven’t reached the
Filter yet, and therefore have reason to fear.
In line with this hypothesis any positive result we get from SETI would be bad news, for
it means that since life is common, especially intelligent life, that
the Filter therefore lies ahead of us, and any negative results we get
from SETI are good news, for the Filter is long behind us.
Given the likelihood that we are not alone in the universe, what this means is that we have reason to fear for our future, and given that we are currently bombarding ourselves with a number of different threats (nuclear Armageddon and global warming being the two foremost threats we are currently subjecting ourselves to), the Great Filter may not lay that far off in our future.
Some compelling content from Mr John Michael Godier, this time he covers “10 Unsettling Solar System Possibilities.” Personally the one I found the most compelling concerned the possibility of life in the atmosphere of Venus, which I will elaborate on below:
It is known for a fact that Venus once had liquid water on its surface, like how Mars used to and how Earth currently does, and it is a fact that Venus has long since lost that water, with the surface of Venus now being a “hellish, heated wasteland” unsuitable for life. But in the atmosphere of Venus there exists a place suitable enough for extremophiles to exist, being at roughly the same atmospheric pressure as the surface of the Earth currently is.
It is possible that some life survived to call this portion of the Venusian atmosphere home, after all, microbes have been found living high up in the atmosphere of Earth as well, what’s to prevent some extremophiles from living in the atmosphere of Venus?
And as the old saying goes, life always finds a way. I once brought up an argument based off of simple thermodynamics that abiogenesis is inevitable. So even though we don’t know for certain that life developed on Venus, this argument further bolsters my case.
We may have even detected possible evidence of microbial life in the atmosphere of Venus, when NASA was undergoing its usual scanning of Venus they detected small blots wherein UV was prevented from reaching the surface of Venus, and UV-absorbing microbes have been offered up as a possible explanation for this anomaly, and would also explain where these hypothetical microbes get their food, they metabolize UV radiation as an energy source.
 For a link to the cited paper proposing that argument in question, see here.