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What is your opinion of the arguments made in "Rare Earth". The Drake equation only gives the upside, but doesn't seem to take into account the conditions that would preclude higher forms of life. For instance, the radiation conditions in the core of galaxies and in the arms of spiral galaxies are too high to allow the survival of higher life forms. That leaves the area between the arms for habitable zones in spiral galaxies, and stars only stay in between the spiral arms for extended periods of time if they are 1/2 the radius of the galaxy from the center of the galaxy. These factors alone remove several orders of magnitude from the number of possible stars that could sustain higher forms of life.

As I stated earlier; there is at least one data point for life in the Galaxy/Universe. Us! Even if all life is confined to these sparse regions of the galaxy, there could be huge numbers of life producing planets. And that is just in our galaxy alone.

They fall out side the life zone and/or are not the correct size to sustain an atmosphere. We are just beginning to explore our own neighborhood.

This is the point of Rare Earth. The idea behind the Drake equation properly applied, means that the habitable zones of galaxies, combined with the number of stable stars, with gas giant in circular orbits, combined with the number of solar systems with rocky planets with the right atmosphere and the correct distance from their star, plus dozens of other factors necessary for advanced life forms, whittles away at the billions and billions of stars, until it becomes improbable that there are other inhabitable planets let alone ones with advanced life.

For the record, I do not believe there are life bearing planets out there; however, I do suspect there are.

I'm not sure I understand what you were trying to say with that statement.