If you don't behave strictly when in standards mode, how will people ever write valid HTML?Sorry dude, that's a false question. "Writing Valid HTML" is like "burning clean coal." It can sort of be done, but there's always something making it dirty, or systems that are so draconian that they sap out the value of the resource (be it coal energy, or perfectly valid XHTML).
Human nature, poor markup rendering engines that are widely spread, and idiotic decisions like making XHTML 2.0 not be backwards compatible, will make "strict" the sigma seven on the curve of diminishing returns.
Should we try to write valid markup, and assume it will be rendered with tender loving care? Of course! And I think Dave's efforts, to make that a reality by following reason and altruistic goals, are good efforts. Unfortunately, browsers can't trust the markup they will have to render, and web developers can't trust browsers not to be quirky (or completely stupid).
Should strict mode be "less quirky" mode or should strict mode be "if it isn't perfect, it's going to be an f'ing mess" mode?