Why alien life would be our doom: Kurzgesagt – In a Nutshell video

Why would the discovery of extraterrestrial life be horrible for life on earth?

The latest Kurzgesagt – In a Nutshell video says there are 10 billion earth-like planets in the Milky Way. If they have or had life on them they should have colonized the galaxy. The fact that they haven't means that either we are alone in the galaxy or there is some kind of deadly "filter" (nuclear war, nanotech, AI, resource depletion) that wipes out advanced life before it's able to colonize the galaxy.