> If the TMT costs X, then the 100-MT should cost about 11X, and with the 15% doubling factor, its ~15X for only a 3X increase in radius.

The Thirty Meter Telescope cost $1 billion. So the 100 Metre Overwhelmingly Large Telescope would cost ~$15 billion using your ~15x multiplier. That's large, but for perspective: The F-35 fighter jet program cost $168 billion.

Like with the Large Hadron Collider, if the extra cost means the difference between being able to crucially measure the atmospheric spectra of nearby exosolar planets and not being able to, then the extra cost is worth it.

I'll take getting definite answers to humanity's most pressing questions, over new tools for killing people, any day.