I agree with the abstract point of the post, but I think it's unrelated to what Rose is talking about. As I interpreted the quote, Rose isn't concerned with how internally playing Devil's Advocate influences individual beliefs; he's interested in whether publicly playing Devil's Advocate is a good thing for the public understanding of the truth. The view he attributes to Dawkins is that publicly playing Devil's Advocate is always bad, because members of the Other Side who are prone to rationalization will readily (though wrongly) interpret it as definitive support for their position. (This is a defensible position even if you have real doubt about your own side, as you can still believe that the evidence points more to your side than any of the others--and therefore oppose actions that will lead people to think otherwise.)
I think you and Rose may be defining "Devil's Advocate" differently. I've usually heard the phrase used to preface the presentation of evidence that goes against a group's consensus. If a discussion group has just decided, after considering the issue, that there is probably no cake in the asteroid belt, someone might mention some additional pro-cake arguments with the disclaimer "I'm just playing the Devil's Advocate..." This doesn't mean that they're engaging in some special, cognitively different task where they actively try to take the perspective of a cake-believer, or come up with arguments in a "rationalizing" manner. It may just be reasoned consideration--the exact same sort of thinking that led them to their no-cake conclusion--that happens to support the cake idea, and the phrase "Devil's Advocate" just reminds the group that the speaker still remembers the anti-cake thrust of the overall evidence. In other words, once people come to a conclusion (particularly one that is emotionally or politically sensitive), they seem to file all evidence for the other side--as in true, good evidence--under the label of "Devil's Advocate." I get the feeling that this is what Rose meant. He wasn't rationalizing, he was just publicly presenting evidence that supports a conclusion he didn't believe.
I agree with the abstract point of the post, but I think it's unrelated to what Rose is talking about. As I interpreted the quote, Rose isn't concerned with how internally playing Devil's Advocate influences individual beliefs; he's interested in whether publicly playing Devil's Advocate is a good thing for the public understanding of the truth. The view he attributes to Dawkins is that publicly playing Devil's Advocate is always bad, because members of the Other Side who are prone to rationalization will readily (though wrongly) interpret it as definitive support for their position. (This is a defensible position even if you have real doubt about your own side, as you can still believe that the evidence points more to your side than any of the others--and therefore oppose actions that will lead people to think otherwise.)
I think you and Rose may be defining "Devil's Advocate" differently. I've usually heard the phrase used to preface the presentation of evidence that goes against a group's consensus. If a discussion group has just decided, after considering the issue, that there is probably no cake in the asteroid belt, someone might mention some additional pro-cake arguments with the disclaimer "I'm just playing the Devil's Advocate..." This doesn't mean that they're engaging in some special, cognitively different task where they actively try to take the perspective of a cake-believer, or come up with arguments in a "rationalizing" manner. It may just be reasoned consideration--the exact same sort of thinking that led them to their no-cake conclusion--that happens to support the cake idea, and the phrase "Devil's Advocate" just reminds the group that the speaker still remembers the anti-cake thrust of the overall evidence. In other words, once people come to a conclusion (particularly one that is emotionally or politically sensitive), they seem to file all evidence for the other side--as in true, good evidence--under the label of "Devil's Advocate." I get the feeling that this is what Rose meant. He wasn't rationalizing, he was just publicly presenting evidence that supports a conclusion he didn't believe.