The problem is, as you said, that it seems Drake and others like the sound of billions of stars in billion of galaxies, but when it comes to an unknown number for existence of life in a planet they pick a very optimistic number, to justify their thesis of abundance of life in universe.
Maybe they take the earth as an example, the life existing under very harsh conditions and deduce that it should be a good probability given enough time. But I am skeptical of this.
Maybe they take the earth as an example, the life existing under very harsh conditions and deduce that it should be a good probability given enough time. But I am skeptical of this.