So we have discovered an Earth-like planet 500 light-years away and Andrew Snyder-Beattie thinks if we found intelligent life on it, it would be bad news for humanity.
I think the argument goes like this:
1) If there is intelligent life on many other planets we should have heard from some of them by now (the Fermi Paradox) so either life is a very rare (or even unique) occurrence - or when it does occur it doesn't last long enough to communicate with us.
2) Assuming life is not a rare occurrence then it must frequently become extinct at some point before evolving to a level with an ability (or desire) to communicate with other planets. When that extinction most often happens is crucial.
3) Any civilisation which produces the technology for communication with other planets would also be likely produce the technology for its own destruction.
4) If the extinction most often happens before the evolution if intelligent lifeforms then we can't expect to find many other planets with intelligent life.
5) If the extinction happens after the evolution of intelligent life then it may be as a consequence of that intelligence (e.g. in developing suicidal technologies).
6) So if we find intelligent life on Kepler-186f* or other habitable planets, this suggests 5) is more likely than 4) in other words it's bad news for us since if we follow the path of the rest of the universe we are likely to ultimately destroy ourselves.
* or rather that there was 500 years ago.