A while ago, I began my review of Menachem Kellner's Must A Jew Believe Anything? (Read part one at this link). I mentioned how the first six chapters of the book are a superb analysis of the role of dogma in Judaism, showing how Rambam's emphasis on dogma was an aberration from normative Judaism. The seventh and final chapter of the book forms a separate unit; it is Professor Kellner's personal view as to what to do with this information.
Professor Kellner's idea is as follows. Once one realizes that defining "being a Jew in good standing" based on adherence to Maimonidean dogma is an aberrant and problematic definition, then we are left with defining a good Jew based on halachic observance. But nobody keeps absolutely every halachah, and nor is there anyone who does no mitzvos at all. Thus, we have a continuum of observance, extending over Orthodox, Conservative, and Reform Jews. While we do not agree with the theology of Conservative and Reform, we can increase our cooperation and unity with them via this insight.
Here is where I must part company with Professor Kellner (notwithstanding my tremendous respect for him and his superb books). My critique is very similar to that raised by Daniel Statman, which Prof. Kellner himself cites and discusses in the afterword to the second edition of his book, but to which he does not, in my opinion, present an adequate response. It seems to me that traditionally, Judaism did not define "being a good Jew" either in terms of adherence to Maimonidean-style dogma or in terms of counting how many mitzvos one performs. Instead, it was based upon commitment and loyalty to the halachic community.
There may well be a continuum of halachic observance amongst all the different flavors of Jews. But there is nevertheless a clear difference between someone who is, in principle, committed to the traditional halachic community (albeit with various lapses) and someone who is not committed to it. (This is not affected by a gray area surrounding the extreme left-wing of Orthodoxy. The gray area simply means that people disagree as to where to draw the line. But all agree that the line itself revolves around commitment to the halachic community.) If a person lapses in his personal observance, he is not undermining the community. But if he supports a rival system (such as the Sadducees and Karaites in ancient times, or Conservative and Reform in modern times), he is undermining the community, and is thus appropriately rejected.
This also applies to the realm of belief. While Judaism as a religion is certainly based upon certain beliefs, and many Torah scholars have discussed what those beliefs should be, we have never cared that much either about the precise parameters of these beliefs, or about what actually goes on inside a given person's head. That is between man and God; we have never grilled people and nor would we ever administer a lie-detector test to people. Instead, what Judaism demands is loyalty to the community and not undermining it. If one expresses beliefs (or lack thereof) in such a way as to undermine the community, he is ostracized. Otherwise, no matter what the person believes privately, he remains a member in good standing.
Kellner sort of acknowledges all this in his discussion of Statman's critique on pp. 136-140, but maintains that there is much to be gained by defining membership in terms of behavior rather than belief, and that excluding people based on their being "public enemies" is untrue to the teachings of Rabbinic Judaism. I disagree - I think that this is how Judaism always operated, either consciously or subconsciously. As for his claim that the new challenges in the modern era require a different sort of response than that given to Sadducees and Karaites, I remain unconvinced.
On a related note, Kellner discusses the critique of Rabbi Dr. David Berger, who insists that Judaism was always defined by dogma. Kellner responds by citing the example of Chabad. He points out that Berger has satisfactorily proved that the extreme strain of Messianism in Chabad is heretical, and yet the rest of Orthodoxy has not excommunicated these people; all members of Chabad are still members of good standing in the community of Israel. Kellner argues that this shows that, at least subconsciously, everyone agrees with him that mitzvah-observance is the true definition of membership in good standing, not theology.
I disagree. The reason why the theological aberrations of the extreme Messianists of Chabad are tolerated is that these people are not still members of good standing in the community of Israel; instead, they are members of good standing in the community of Chabad. Chabad is so isolated from the rest of Orthodoxy that the extreme Messianists can simply be ignored. I guarantee that if Chabad were to start missionary work with the rest of Orthodoxy, they would be banned faster than you can say Slifkin.
All this is not to say that I believe Kellner's efforts in the first six chapters to be wasted. On the contrary; I think that they are extremely useful, and I think that every reader of this website should read Must A Jew Believe Anything?. But in my view, the concepts of the first six chapters are useful in a different way than Kellner proposes. I have briefly mentioned my ideas above, and I plan to discuss them in more detail on a future occasion.