re: Fermi Paradox is a point against that theory
If conventional expansion into the galaxy occurs by intelligent life, we should see signs of other intelligent life by now. That is the basis of the Fermi paradox. I'm in the camp that the explanation of the Fermi paradox lies in some natural maturation of intelligence that eschews conventional expansion. I don't know if a superintelligence that evolves may go to another dimension or what, but something big happens that makes expansion into our "known" physical universe irrelevant.
And maybe there are no other 'intelligences' anywhere.