justification for producing valid [X]HTML?

I'm trying to make a justification to management why our organization
should care about producing valid [X]HTML.

The current attitude is:

    1.  We design our documents for a consistent "look and feel"
        (using mostly WYSIWYG HTML editors).

    2.  Our documents render "properly" in Netscape/Mozilla/IE.

    3.  Why bother to take the extra time to produce valid HTML when
        the "invalid" HTML works just fine?

I'm sure people have written documents to refute these types of
attitudes.  Unfortunately, I'm having very little luck in performing
web searches for such documents, because the phrase "valid HTML"
appears on about a billion web pages.

Can anyone point me to a URI that will neatly refute the above
attitudes?

(Note: PLEASE DO NOT POST A FOLLOW-UP TO ARGUE WITH THE ABOVE POINTS.
You're preaching to the choir.  I need a concise and detailed
document, and I don't feel that I have quite enough web experience to
write one myself.)

Thanks in advance for any pointers.