Sorry, but you'll have to wait another day for part II of the Scientific Ethicist.
Blame SteveG for making yet another thought-provoking post from Philosopher's Playground: The Charlie Brown-ization of Political Ethics (17 Jan 2007). Steve correctly identifies an important issue, but I think his evaluation and proposed cure are somewhat naive.
Steve identifies several rhetorical tactics in political discourse and focuses on two: framing and caging.
Framing is the description of some specific issue using words which have ethical or value connotations advantageous to your own position. The classic example is the the framing of abortion rights by proponents in terms of choice and by opponents in terms of life.
Caging is focusing attention on one particular instance out of many in a class, an instance where your own side's position is strong (or one you can most easily frame advantageously) and suppressing attention on the instances which are less advantageous. Steve offers the example of caging the general issue of [racial] civil rights by focusing on affirmative action in hiring. It's also helpful, he concludes, that caging be intentionally pursued uncivilly and with extreme passion to make one's opponents look weak, pathetic and vulnerable if they attempt to simply ignore the focus.
Steve's analysis of these tactics is spot on. But his evaluation of what these tactics mean is naive. Caging especially, he asserts, "undermine[s] ethical conversation." He proposes reasoned discourse as a cure, a "measured, careful discussion; one that treats all concerns open-mindedly and which allows for careful, creative alternatives to be considered." An admirable attitude, to be sure, but naive and dependent on a faulty premise.
The faulty premise is that ethics (in the particular) can be objectively true, allowing reasoned discussion to find that truth. But the problem is that particular ethical statements can't be objectively true in the same sense that particular statements about reality can be objectively truth, or even in the same sense that scientific theories can be objectively true. Seeking a truth that simply does not exist is, of course, an exercise in futility.
Any specific ethical theory fundamentally depends on the actual values which real people hold subjectively as mental states. Thus there are only two effective ways of talking about ethics in the particular: propaganda, the attempt to inculcate particular values in the audience, and negotiation, the process by which two parties with differing values agree on actions which will maximize the mutual satisfaction of their values. Reasoned discourse is at best a peripheral technique and at worst completely irrelevant.
The conservative movement has achieved notable success precisely because they have grasped this fundamental meta-ethical truth. Although people sincerely holding core conservative values are a relatively small minority, the conservative movement relentlessly propagandizes derivative values to engender support for their core values and uses the success of this propaganda as a powerful negotiating tool.
Conservatives use framing and caging effectively. Few outside the core conservative movement favor outright racial discrimination. Rather than ineffectually try to propagandize this underlying value, the conservative movement propagandizes the derivative value of "equal" employment opportunity framed in a way that supports the core value. No one is for outright sexual enslavement of women (i.e. "barefoot and pregnant"), so they propagandize respect for life also framed in a way that supports the core value.. And the framing device of "personal responsibility" has been tremendously effective.
Since there is no particular ethical objective truth to be found, calm, reasoned discourse cannot be a panacea (although it can be effective as propaganda or negotiation). Rather, progressives and liberals have to bite the bullet and explicitly and unashamedly use propaganda and negotiation. We have to sell our values, and negotiate with those who aren't buying.
Resorting to propaganda doesn't mean that liberals and progressives have to sink to the level of conservatives in ethical discourse. Propaganda is a word loaded with negative connotations; worse yet it has no good synonyms. Ethical objectivists have shot themselves in the foot by framing "propaganda" so negatively; by trying conscientiously to avoid propaganda in favor of "rational discourse", intelligent liberal people deprive themselves of a fundamental tool of ethical discourse.
But propaganda does not have to be bad, it does not have to be dishonest, it does not have to be slimy in any way. Look at King's "I Have a Dream" speech: It's pure propaganda, inculcating the values of human dignity and racial equality in his listeners. He's not making any sort of logical argument from true premises, but there's nothing slimy, dishonest, or covert about it. He's right up front about the values that he wants his audience to embrace. Indeed the whole Civil Rights movement in the 60's was as effective as it was precisely because King was both a master propagandist as well as a tough negotiator.
Propaganda per se is not undermining political and ethical discourse; it's a necessary part of ethical discourse. Not even dishonest propaganda is undermining discourse: Sincere, honest propaganda will beat disingenuous and dishonest propaganda every time (even Hitler and Goebbels were right up front about the whole "kill all the Jews and take over the world" thing).
What's undermining political and ethical discourse is the shame towards which the progressives and liberals approach the idea of propaganda. Any attempt to sell our values is seen as unseemly and embarrassing. Leaving the propaganda field wide open to conservatives and authoritarians allows them get away with using dishonest propaganda.
Our liberal, progressive values are rational and true, are they not? Sadly no, not any more than conservative values are "rational" and "true". Values are not truths, they are facts, facts about human minds. And they are contingent facts, facts which can be changed in the same sense that a fact about the position of an object can be changed by moving it.
There is no magic bullet--not even reasonability--for ethical discourse. Ethical discourse is a project and a conflict; there are battles lost and won, progress made and losses suffered. Liberals and progressives should, of course, be ashamed to use dishonest propaganda. But we should not be ashamed to use propaganda, to sell our values honestly, sincerely and, most of all effectively.
Of course, Tom Tomorrow makes a similar point a thousand times more succinctly than I do.
 I don't want to sound like I'm putting down reasoned discourse universally. If you want to discuss scientific truth, logical analysis, mathematical theorems, or the best way to get to Minneapolis, there's just no substitute. But it is precisely the same features of reasoned discourse which make it suitable for discussions about objective reality that render it unsuitable (in many senses) for discussions about subjective values.
 I don't think the conservative movement has anything "personal" against black people and women (nor homosexuals, laborers, the middle class, atheists, heretics, Jews, etc.). But oppressing and exploiting such people are "traditional" values which people self-described as "conservative" might logically be expected to conserve.
 See Andrew Sullivan, for instance: "[R]ational thought, not revelation, is all that is required to arrive at the fundamental conservative principles of personal responsibility and the rule of law." (Vive La Resistance, 15 Jan 2007)
This statement is not only wrong, it's trivially stupid: Outside of completely uncontroversial interpretations, both "personal responsibility" and "rule of law" are vacuous in their literal sense, mutually contradictory and so metaphorically flexible that together they can be used to "justify" anything from anarcho-communism to totalitarian fascism.
Also see George Scialabba's excellent essay The Work Cut Out for Us for an example of how conservatives use "personal responsibility" as a framing device.
 i.e. Even if you don't buy into this whole "human dignity" business, you'd better reach some sort of accommodation with those who do or you're going to have thousands of uppity (but well-dressed) Negroes marching in your streets, boycotting your buses and taking over your lunch counters.
 Kindly untwist your knickers; I'm using the term as a sarcastic jibe towards racists.