Type III Societies (Apparently) Do Not Exist

[Abridged] Whether technological societies remain small and planet-bound like our own, or ultimately span across galaxies is an open question in the Search for Extraterrestrial Intelligence. Societies that engineer on a galactic scale are classified as Type III on Kardashev's scale. I argue that Type III societies can take the form of blackboxes, entire galaxies veiled in an opaque screen. A blackbox has a temperature that is just above that of the cosmic microwave background. The screen can be made from artificial dust pervading the galaxy. I show that there is enough material in galaxies to build blackboxes if the dust is fashioned into dipole antennas. The thermal emission of a blackbox makes it a bright microwave source. I examine the Planck Catalog of Compact Sources to constrain the abundance of blackboxes. None of the 100 GHz sources has the spectrum expected of a blackbox. The null result rules out shrouded galaxy clusters out to z ~ 1 and shrouded Milky Ways out to (comoving) 700 Mpc. The reach of the results includes 3 million galaxies containing an estimated 300 quadrillion terrestrial planets, as well as tens of thousands of galaxy clusters. Combined with the null results from other searches for Type III societies, I conclude that they are so rare that they basically do not exist within the observable Universe. A hypothesis of "Cosmic Pessimism" is discussed, in which we are alone, our long-term chances for survival are slim, and if we do survive, our future history will be checkered. Our loneliness is suggested by the lack of Type III societies. I discuss the remaining forms of Type III societies not yet well constrained by observation. I argue that the ease of building blackboxes on planetary and Solar System scales may lead, within a few centuries, to environmental catastrophes vastly more devastating than anything we are doing now, boding ill for us.