Is the rationale for building the TMT rational?
Both sides of the Thirty Meter Telescope debate have been generally favorable to both astronomy and the telescope, with the main objection being that the telescope should not go on Mauna Kea.
It is widely accepted that astronomy is an important science, and that the TMT would be the biggest and best telescope.
Of all the sciences, astronomy has the least practical importance. Astronomy has virtually no chance of discovering anything that would have the slightest material effect on anybody.
Defenders of astronomy (the necessity of a defense says a lot) can only point to a few spin-offs from technological advances in equipment that almost certainly would have been discovered without astronomy.
The Milky Way Shines over snowy La Silla Observatory, Chile, 2013.
Flickr: European Southern Observatory
Even within the field of astronomy, there is no real need for the TMT.
A consortium of 16 European nations has already begun construction in Chile on the similar but considerably larger (39.3 meters) Extremely Large Telescope.
Its mirrors will have about 70% more reflecting area than the proposed TMT.
There doesn’t appear to be much the TMT would contribute to astronomy that the ELT cannot do better.