If I may... If you google me you will find old old reasons to hate me,
and those reasons are connected to GUIs. I do know one or two thinks
about the subject.

It is possible to make a good GUI that is separated
from its functionality in the manner many contributors to this thread
are thinking of. But it has a touch of RFC1925 compliance: "Pigs fly
just fine, given sufficient thrust." Committees like to design such
things, implementing them is hard work.

An example may make it
clearer:

You have all seen disabled menu items. Those often correspond
to CLI switches that lead to error messages in a given situation. But
there is a difference: using the CLI switched lead to an error message
when the user issues a command, while the menu items have to be
disabled before the user issues the command.

A GUI generally needs
much closer contact with the object it manipulates before it issues a
command than a CLI does. The CLI needs better error error reporting for
actions that fail, the GUI needs much more information ahead of time...
if it is to be good. There are other differences as well, e.g. good
GUIs divide complex operations up into simpler ones in a manner that
does not quite resemble good CLIs.

Writing sucky code is easy. But who
wants to do that.

Arnt