Dennett's arguments against greedy reductionism - something to the effect that human behavior is just the terminus of evolution and natural selection - leads nicely into his chapter On The Origin of Morality.  (Darwin's Dangerous Idea - Chapter 17).  Dennett lays out the framework of the question succinctly:

"Mathematics and physics are the same for everyone everywhere, but ethics has not yet settled into a similar reflective equilibrium.  Why not?  Is the goal illusory?  Is morality just a matter of subjective taste (and political power)?  Are there no discoverable and confirmable ethical truths, no forced moved or Good Tricks?  Great edifices of ethical theory have  been constructed, criticized and defended, revised and extended by the best methods of rational inquiry, and among these artifacts of human reasoning are some of the most magnificent creations of culture, but they do not yet command the untroubled ascent of all those who have studied them carefully."

 I was looking forward to Dennett's chapter on ethics much like I enjoy seeing a star athlete substituted in for a normal player - he has a great capacity for navigating some difficult territory.  I doubt, however, that Dennett would claim that anything in the chapter dents the framework of uncertainty that he detailed above.   In fact, we move rather dismissively through Utilitarianism and the Kantian Categorical Imperative into a somewhat meandering discussion of how decisions with ethical implications actually do proceed. 

Time constraints, psychology, self-doubt, and conversation stoppers are key ingredients in detailing ethical stories for Dennett.  The conversation stopper such as, "That would do more harm than good" leads to "temporary equilibria" in a shared decision making process with ethical implications, and it is these meta-memes, and the process wherein society defines them, that warrants our attention. 

So, Dennett tells us not to despair: the complexities of how real ethical questions unfold over time, and the ambiguity in applying maxims in such circumstances, practically, and probably theoretically, prohibit an a priori maxim or framework from being of the cornerstone of our decision making in these matters, but that, despite greedy reductionist attempts, the meta-memes we create are sufficient.  We are ever-searching for better solutions to our ethical issues and that creates our ethical foundation.

I think there is still quite a bit to despair of here: whose meta-memes and why?  The dismissal of the Categorical Imperative - the test of universal law for any decision - is based on there being too many candidate maxims, although Dennett stresses the temporality of ethical decision making.  He hasn't convincingly dismissed the Categorical Imperative, on my view.