As a point of order, who says that PCs need be of heroic stamp? that's a matter for the players to determine, they and none other, most assuredly.The quote in question is from a 2005 Q&A thread with Gary Gygax and can be found here.
ADDENDUM: Let me say that my own feeling is that D&D -- or, indeed, most RPGs -- ought be "agnostic" on the question of end and means, leaving such matters up to the players and referee to decide for themselves. Such agnosticism is a strength, enabling groups to play the game according to their own tastes rather than those of its designers.
ADDENDUM #2: John Laviolette posted a very astute comment on this discussion over at his blog, where he reminds us that "villain" is not the only antonym for "hero."