This is a bit of a sticky issue. How can the movements of Judaism which do not recognize the divine authority of the mitzvot or the standing of rabbis to declare judgment in Halacha still maintain a sense of obligation to Jewish heritage and traditional Jewish practices? What is the place of Halacha in a philosophy that does not recognize divine law? Simply, on what basis can liberal Judaism make requirements on their constituents?
A major problem of Reform and Conservative Judaism is the apparent "anything goes" approach to Jewish practice and belief which leads to a free for all and disintegration of Jewish identity and community. This approach is based on the ill-conceived idea that people will leave Judaism entirely if they feel the least bit chaffed by obligations that do not suit them, yet it is those people who are most likely to be committed to Judaism which then feel little for it because it requires nothing of them. Judaism becomes meaningless. Liberal movements tend to play towards the lowest common denominator in order to create the biggest tent, but ultimately this backfires as the content of Judaism is lost in empty aphorisms and continually dated political efforts. The process promotes a weakness in Judaism to which even committed Jews have trouble finding tangible connection.
So I have an approach which is akin to some Reconstructionist approaches where it is Jewish heritage itself that makes claims on each Jew. A committed - religious - Jew is one who delves into the richness of our history, religious evolution and traditional practices in order to make a home for themselves in our heritage - and, most importantly, is keen on passing on that sense of patrimony to the next generation. The idea is that one is not just a passive receiver of a heritage, but one has an obligation to maintain it, make it one's own and pass it on. The mandate is to build a Jewish philosophy, a Jewish family and a Jewish community. This necessarily applies to both individuals and the larger collective as the goals cannot be met by a kahal without individual interest, nor can an individual best express his Jewishness without communal life.
B. Spinoza elsewhere lambasted this approach as being little more realistic than divine obligation. That a heritage cannot create an obligation. I disagree (obviously). A Jew is defined by his heritage - since it is only our heritage which makes us different from any goy on the street and therefore it is by our heritage that we can judge whether a person is a good or a bad Jew. First and foremost is how importantly a Jew considers his heritage to be - indeed, how important a Jew believes it is to be a Jew. Any individual Jew may be a great person, but if he doesn't take his heritage seriously and doesn't care to pass it onto his children, then he (I'm sorry to say) simply isn't a great Jew.
Now I believe that once a person really takes his identity seriously, a next step is to follow a way of life that best exemplifies the values so accepted. Following some approximation of traditional Jewish practice - orthopraxy - seems like an ideal fit to me. What precisely the borders of Halacha ought to be in such a state is essentially a matter of politics, though some general principles need to be followed in order for communities to coherently exist. Personally I tend towards relatively more conservative realizations of Jewish practice, but these are details.