The following statements are in support of the JWST and come from a variety of sources. If you take issue with the validity of a statement, then please leave a comment and we will research the issue. Emphasis via font changes, color, and other enhancements are those of the authors of this blog and NOT the original sources of the statements:

What it failed to remark is that the telescope’s hardware is 70 percent complete, much of it has already undergone testing and a special commission established to look into the telescope in 2010 found that the work on technology was “commendable and often excellent.” Billions of dollars would not be wasted by continuing the project. They would be wasted by canceling it.
- The Washington Post

When we started Hubble, dark energy didn't exist. At least, we didn't know about it [...] When we launched Hubble, there was no such thing as extrasolar planets. So those kinds of discoveries would probably go lacking, unless some other nation stepped forward and did it.
- Charlie Bolden, head of NASA to Congress, via this Scientific American Article

While it is undeniable that the project has had large cost overruns and is behind schedule, it is also very clear that the project will once complete be a tool of enormous worth to the scientific community — and, through them, to the general population — not just in the U.S. but in the entire world.
- Matt Blum, writing through GeekDad in a article

This not only threatens the future of science research, but it will have a dramatic impact on our economy, costing 2,000 full-time private sector jobs in 22 states.
- House Minority Whip Steny H. Hoyer (D-Dist. 5) of Maryland via this article

The Webb Telescope will lead to the kind of innovation and discovery that have made America great. It will inspire America's next generation of scientists and innovators that will have the new ideas that lead to the new jobs in our new economy
- Senator Barbara Mikulski via her official Senate Webpage

JWST will lay the foundation on which a better understanding of the early universe will be built [...] It has the potential to transform astronomy even more than the Hubble Space Telescope did, and it will serve thousands of astronomers in the decades ahead. We cannot abandon it now.
- AAS President Dr. Debra M. Elmegreen via the American Astronomical Society website

Almost 20 years ago, Congress cancelled what was then the most ambitious scientific project ever launched: the Superconducting Super Collider. The particle collider, the world's largest, would have resolved questions ranging from the origin of all mass to the nature of fundamental forces. But cost overruns and management issues gave a Democratic Congress an excuse to kill the program during hard economic times. A similar situation has now arisen—and it's threatening to ground the nearly completed James Webb Space Telescope.
 - Lawrence M. Krauss writing in the Wall Street Journal

There is no mission planned by any other space agency that can achieve the science goals of JWST. These goals are transformative and will open a new era in astrophysics: JWST will find liquid water on planets, reveal the births of stars and planetary systems, and study the evolution of galaxies.
 - Northrop Grumman, from their website in support of the JWST

Exploring the early universe presents a unique challenge for astronomical observations. The starlight from the first galaxies arrives at earth as infrared radiation, while the extreme distances involved render ordinary galaxies nearly invisible to either Hubble or large telescopes on the ground. The next steps along the path of discovery must therefore be taken with an infrared, space-based telescope with unprecedented sensitivity. The James Webb Space Telescope will have this unique capability.
 - A statement regarding the future of the James Webb Space Telescope from the ~140 Delegates of the “New Horizons for High Redshifts” meeting, held at the Institute of Astronomy, University of Cambridge
July 25-29, 2011

In July 2011, NASA finished polishing the new space telescope’s mirrors to an accuracy of one-millionth of an inch, a milestone toward its completion. The technology developed for testing the mirrors has already spurred improvements in ocular health care, from diagnosing problems and providing more accurate contact lenses to perfecting laser eye surgery, according to NASA.