So I'm going to quote from Rabbi Zemer's "Evolving Halacha" (a Conservative position on halchah), and whenever you see a highlighted "NOTE" that's my opinion on whether we need to diverge from the stated "principle". Also, some definitions: (1) d'oraita refers to authority from Scripture; (2) d'rabbanan refers to what I feel is the lesser authority of rabbinic law (I feel it is a secondary authority and that all Scripture, including the Apostolic Writings, is the primary authority).
Here it is:
PRINCIPLES OF CONSERVATIVE HALACHAH
pg. 45 "The sections that follow review several principles and criteria for determining the halakhic attitude appropriate for modernist Jews. These principles have been gleaned from the writings of many thinkers affiliated with various streams of Judaish--Reform, Orthodox, Conservative....Although these criteria are not stated explicitly in the codified Halakhah, they are implicit in it and can be deduced from it."
pg. 46 "Halakhah Is an Evolutionary Process....This concept of change and development may serve as a guide for modern Jews in assessing those mitzvot that evolved over time and are therefore relevant to our day."
NOTE: No man has the autonomous authority to disregard mitzvot d'oraita.
pg. 46 "Halakhah is Pluralistic...Historical research proves that Jewish law was always diverse in nature and certainly far from monolithic. During the controversy between Beit Hillel and Beit Shammai about forbidden marriages, the two schools did not refrain from intermarrying, even though a particular union might be forbidden according to the halakhic ruling of one school but permitted by the other.
Yitzhak Gilat, professor of Talmud at Bar-Ilan University, pointed out that in spirt of the great differences between the two schools, they came to the recognition that 'both [rulings] are the words of the living God' (BT Eruvin 13b) and that a person could act according to either view: 'Whoever wishes to conduct himself according to Beit Shammai may do so, and according to Beit Hillel may do so' (ibid., 10b).
This freedom of halakhic ruling was accepted in practice during the time of the Second Temple. In the words of Prof. Gilat, 'every Sage was permitted to render decisions in his town and home according to his own tradition and in consonance with his judgment, on the basis of the deliberations in the rabbinic sources.'
....Pluralism can be found in many codifications and rulings--for example, the hundreds of disagreements between Maimonides and his most prominent commentator-critic, Rabbi Abraham ibn Daoud...
Maimonides and the tosafists disagreed as to whether Christians should be considered to be idolaters. Maimonides, who spent all his life among Muslims, said they were. By contrast, Rabbenu Jacob Tam, the most prominent of the tosafists, who lived in Christian France in the twelfth and thirteenth centuries, ruled that Christians could be believed on oath because 'they have the Creator of Heaven in mind.'"
NOTE: I agree.
pg. 49 "If a ruling is halakhic, it must be ethical. If it is unethical, it cannot be halakhic."
NOTE: this is fine with matters d'rabbanan but completely unworkable with d'oraita.
pg. 50 "The Commandments Embody Holiness...The litmus test of holiness should determine the value of every religious act in the daily life of Jews of our generation."
NOTE: this is completely unworkable and inappropriate.
pg. 50 "Internalizing the Commandments...Is there any place for inner identification with the commandments, or must we be like disciplined soldiers who obey without question or hestitation?
...What I am not yet able to accept may, in time, become acceptable, and therefore a commandment for me. The criterion for the observance of a commandment is whether I can internalize and observe it with full inner devotion and intent. This requires a constant effort of selecting commandments and trying them out."
NOTE: this is fine for d'rabbanan but is completely unacceptable for d'oraita. Does one say of his father's commandments, I'll see how I feel and then maybe I'll obey?
pg. 51 "The Critical Approach to Halakhah...The Sages were undoubtedly scholars of great intellectual power and moral giants, and sincerely devoted to the Torah, but they did not have the scientific tools that have given us access to archeological discoveries, documents from other ancient cultures, and documents from our own past, such as those form Cairo Geniza.
...The British Liberal Rabbi John Rayner has given clear statement to a principle of evolving Halakhah that is infrequently aired:
'There are whole vast areas of Halakhah...predicated on assumptions that are unacceptable to us, for instance, regarding the inferior status of women, the hereditary privileges of the priesthood, the desirability of sacrificial worship, the importance of ritual purity, the defiling effect of menstruation and the legitimacy in principle of capital and corporal punishment....We cannot accord to the classical literary sources of the Halakhah more than a presumptive authority, and therefore what they legislate needs to be weighed against the individual conscience, the needs and consensus of the community, and still other considerations including historical and scientific knowledge as relevant.'
These are among the factors that a modernist Jew should weigh critically when deciding whether to observe a particular commandment."
NOTE: presumptive authority is fine for d'rabbanan authority---provided one engages in a critical evaluation. However, final authority (not merely presumptive) must be given to mitzvot d'oraita.
pg. 53 "The Call of Individual Conscience...Modernist Jews may meticulously observe a large proportion of the precepts ot eh Torah and Sages with a clear conscience, but there are many other precepts that they cannot accept. They are likely to discover that their consciences do not allow them to participate in the ritual of halitzah or the legal fiction of selling one's leavened products to a non-Jew for the duration of Passover."
NOTE: This "principle" illustrates a difference between liberal values and traditional values.
pg. 53 "Responsibility for the Covenant Community...we must all ask ourselves not only whether a particular precept is compatible with our individual world view, but also whether observing it would harm or strengthen the Jewish people as a whole."
NOTE: This is a valid principle.
pg. 55-56 "The Rationale for the Commandments...The nineteenth-century German Rabbi Zacharias Frankel reached two conclusions on the basis of his study of the rationale of the commandments and their significance:
[1] We must respect all the excellent customs handed down to us by our ancestors, while rejecting those that give of a whiff of superstition;
[2] We must continue organically the path of the Sages of the Middle Ages, whose regulations rejuvenated the face of Judaism."
NOTE: it's fine to be critical of the rationale behind the minchagim and to use that in determining continued use of the custom; it's quite another thing to be critical of the rationales of mitzvot d'oraita.