Everyone adopts beliefs for primarily social rather than rational causes. I am a devotee of science, an atheist, a humanist not because I carefully, logically, and thoroughly considered all the pros and cons and made a reasoned decision, but primarily because that's how I was raised. Likewise too, people become supernaturalists, Christians/Muslims/Hindus etc., and moralists because that's how they were raised. We come from a civilization that reaches back five millennia in the written record and probably ten thousand years or more in the oral tradition. It includes millions of people who spent their entire lives thinking carefully, with greater or lesser success, about what it means to be a wise and good human being. I just don't have time to think everything out from first principles, even if I knew what those first principles were. So I, like everyone else, must rely on "secondary sources".
That everyone's beliefs, including my own, are primarily socially constructed does not entail that rationality is superfluous. A rational person is a person who, rather than constructing her beliefs rationally, will eliminate her beliefs when they fail rational scrutiny. I placed my beliefs about capitalism and republican "democracy" came under critical scrutiny; I became a communist when they failed the test of rationality. Rationality is an indispensable tool for shaping our beliefs, but by and large rationality shapes our beliefs not positively, by constructing true beliefs, but negatively, by eliminating false beliefs. "When you have eliminated the impossible," says Holmes, "whatever remains, however improbable, must be the truth."
But for rational thought to have an effect, a person must be willing, at least potentially, to abandon any belief, however cherished, if it fails the test of rationality. More importantly, a person must be absolutely opposed to redefining what rationality is just to preserve some cherished belief. Without these twin commitments, which are themselves not rational but fundamentally moral, rationality is entirely ineffective. A person who is not morally committed to employing and preserving rationality will not only fail to be persuaded by a rational argument, but their compromise and corruption of rationality will spread into other domains, diminishing the effectiveness of rationality and critical scrutiny in general. The controversy, such as it is, is not just about what beliefs are more rational, but whether rationality itself, and its integrity, is morally necessary.
Moral discourse is fundamentally different from rational argument. There are no objective, purely logical reasons for any fundamental moral belief. Moral beliefs are not about how the world outside our minds actually is; moral beliefs are about how we want to build the worlds inside our minds. Moral beliefs are about who we want to become, as individuals and as societies. Rationality is not completely irrelevant — many people support or justify their moral beliefs with false statements about objective reality — but at the fundamental level, morality is not about truth but about choices. Because these choices are not about objective truth but about about subjective truth, truth about the inside of our minds, discourse about the objective world, the world outside our minds, is irrelevant.
Even to the extent that people use false statements about the world — black people or women are inferior, the poor are lazy, the rich are virtuous — cool rationality is often ineffectual. Rationality never gives us absolutes; it gives us only more or less possible or plausible. Set your threshold high enough, and any belief can survive rational scrutiny: extraordinary claims do indeed require extraordinary evidence. Furthermore, what precisely constitutes rationality is not given without controversy. How, for example, should we evaluate and understand probability and plausibility? Bayesian? Frequentist? Null-hypothetically? And finally, even where the canons of rationality are more-or-less generally agreed upon by scholars and scientists, the exercise of rationality is technically challenging. You must, as Feynman argues, not just decide not to fool yourself, but always bend over backward not to fool yourself. Rationality requires considerable study and unceasing discipline.
There are many ways to change how people think at a social level. If, like Godless Girl, you want to exclusively employ cool, calm rationality, more power to you. But some of us, myself included, want to use all the tools available. Mockery, derision, and insult really do work, and they can go where pure logical, evidentiary analysis cannot go. If a person is not deluded about the effects of cruelty or the objective nature of the objects of his cruelty — and, I think, many cruel people are not so deluded — I cannot persuade him that cruelty is in any sense "false". All I can do is tell him, in no uncertain terms, that I violently disapprove of his cruelty, that I, and others like me, will mock, belittle and ostracize him for his cruelty, and, if sufficiently provoked, react coercively. We do not, for example, have a philosophical conversation with a murderer, rationally convince him of the error of his ways, and then turn him loose; once we have rationally determined that it's objectively true that he committed murder, we punish him. (I do not advocate such extreme measures as coercive punishment in the discourse about religion, superstition, or politics. But I advocate lesser measures not because anything but pure rationality is immoral but because extreme measures are usually disproportionate.) In addition to objective, rational analysis, human beings use shame, guilt, derision, insult, and condemnation no less than praise, approbation, and admiration to affect the social acceptance and rejection of moral ideas. Most directly, derision and insult undermine privilege. Intellectual privilege can be taken to extremes of dogmatism and unquestionable authority, but the sine qua non of intellectual privilege is immunity from the raspberry, that the privileged can say anything, no matter how stupid, and his listeners are automatically compelled to take the idea "seriously" and discuss it "respectfully". Everyone has to earn this kind of respect; it is not automatically granted.
Of course, derision, mockery, and insult are not universally applicable. They are not at all effective in the short term and at the individual level. One cannot change a person's mind by insulting him directly. The effect, rather, is indirect: to undermine the socially constructed intellectual privilege of the speaker and to convince listeners that they too will be mocked, and possibly ostracized, if they express similar beliefs. Derision is ineffective when applied too broadly, because when applied broadly it is often inaccurate, and the rational person, even when using supra-rational tools, still demands accuracy. Finally, derision, mockery, and insult shut down rational discourse because they undermine the necessary presumption of good will; they are most effective when there is sufficient evidence that the target has already fatally compromised rationality and good will. Similarly, although mockery and insult can be applied directly against particularly odious moral opinions, they have additional power when directed not against an opposing opinion, but against the egregious misuse of rational, logical thought supporting that opinion. These tools are limited, but within these limitations, they seem very effective.
I cannot write an essay justifying the use of insult and then take offense that Godless Girl effectively calls me a "douchbag" for behavior that objectively applies to me. The shoe does fit, and I will wear it. It is noteworthy, however, that Godless Girl employs the very tactics she condemns: she identifies behavior that she strongly objects to, and makes it perfectly clear that she does not consider those who use that behavior to be "one of us."* She wants to change social behavior by using insults — e.g. "douchebag", "idiot", "asshole", — to express her disapproval of behavior that she disagrees with. Good for her. I know she and I are not entirely aligned; I am not "one of us" to her. I can live with that.
*Scare quotes, not an actual quotation.