Well, first you must know that there are 5 recognized branches of Judaism:
Orthodox Judaism–including the Haredi (which includes the smaller group of Hasidim) and the Modern Orthodox. Orthodox Jews observe all 613 mitzvot and tend to use the Shulchan Aruch from the 16th century for practical application. Haredi seek to segregate themselves from the wider culture, while Modern Orthodox do not, other than the practice of their religion requires.
Conservative Judaism– no, not politically conservative, but:
Code:
* A dedication to Halakha (collection of Jewish religious Law)
* A deliberately non-fundamentalist teaching of Jewish principles of faith;
* A positive attitude toward modern culture; and,
* An acceptance of both traditional rabbinic modes of study and modern scholarship and critical text study when considering Jewish religious texts.
Reform Judaism–the biggest group of adherents in the US:
This is a marriage of Judaism and Enlightenment philosophy. The practices have changed over time as it is a progressive movement that believes in the constant integration of Jewish tradition and modern life. Personal and community autonomy is highly valued and so practices will vary widely even from one Temple to another.
Reconstructionist Judaism– a newer branch that developed from the teachings of Rabbi Kaplan in the 1920’s. His ideas include:
“Judaism could do well by incorporating the American ideals of equality and democracy. Theological perspectives that flourished in traditional hierarchical societies needed to be reconstructed to speak in a society where authority derived from the people and where one’s religious or ethnic identity was not, in principle, a barrier to full economic and political participation.”
He did promote observance of the Law, but the rituals and rules were made holy by the unity and community of the people performing them, not because they were from the Divine.
He also saw Judaism as a civilization, not just a religion so he wanted the Temple to include programs not just on religion and Torah, but dance, sports …
Reconstructionist Judaism also believes that all religions are man-made, their own no more than any other and that there is no one true way to the Divine.
Humanist Judaism–started in 1963 by Rabbi Wine. It is a non-theistic Judaism. Humanistic Judaism embraces a human-centered philosophy that combines the celebration of Jewish culture and identity with adherence to humanistic values
Now, so why are there “cafeteria” Jews? Consider that the largest group of Jews in the US are Reform Jews. This branch believes in personal autonomy. This is a big difference between the Catholic view that all Christians are in a communion of Saints so you have an obligation to help each other on the way. Reform Jews, on the other hand believe that each Jew’s observance of the Law is his business and we are not to judge or expect to be judged for our observance.