On Fri, 15 Jul 2011 09:29:07 -0700 (PDT), Quadibloc
wrote:

One thing about the JWST that disturbed me was the fact that its
mirrors are coated with gold...

It's an IR telescope. By design. IR isn't just interesting at the
moment, it is key to the scientific intent of the instrument. Trying
to make the JWST do too many things is just asking for problems. And
for IR out to 27um, gold is better than aluminum (and in near IR, it
is a lot better).

Also, the optical system does incorporate adaptive optics, which as
you note is much easier to do with long wavelengths. Making a super
light weight segmented mirror that was diffraction limited in visible
wavelengths would have been much more difficult and expensive.