"Jay Sekulow, Moishe Rosen and Zola Levitt are regarded as Christians, even though they claim to follow all the Jewish laws and customs"
The key word there is CLAIM. In fact, they violate the most basic of the Jewish laws and corrupt Jewish customs by interjecting the worship of a God concept forbidden to Jews.
I don't know the Beastie Boy you speak of, but with regard to Buddhism, it rather depends on the form of Buddhism and how they practice it. Some forms of Buddhism are polytheist ( from the literalist views present in the Dhammapadas) others follow a philosophy of life that is rather without any notion of god concept.
Any Jew who adopts a covenant of faith that is contradictory to Torah they become apostate.
Odd you should mention Spinoza, whose God concept Einstein embraced and is rather at odds with the personal God concept in Torah. Spinoza received a "cherem" , akin to an excommunication for it. That's something so harsh and severe, it is rarely ever done. They've not even issued one for Martin Meyer ( aka Moshe Rosen) as far as I know, despite his being ordained a Baptist Minister and changing the name of the Southern Baptist American Board of Missions to the Jews name to Jesus for Jesus. Perhaps because he had so openly rejected and left the Jewish people they saw no need. Einstein and Spinoza never left.
Einstein was even offered the Presidency of Israel and he traveled the United States raising money for it. “ The pursuit of knowledge for it’s own sake, an almost fanatical love of justice, and the desire for personal independence- these are the features of the Jewish tradition which make me thank my stars that I belong to it.” Albert Einstein
Both Spinoza and Einstein were proud to be Jews. Einstein and Spinoza shared a concept of an impersonal Creative force, not the God concept of Torah despite having both been Torah students as youth. They did not adopt other religions, and were rejected by the Orthodoxy, they did not reject Judaism for another religioin as the Jews who embrace Christianity do.
There are position statements from every Rabbnic council of every Branch of Judaism on the planet that tell us that we are obligated by Jewish law to inform others that someone who misrepresents a belief that is NOT Judaism AS Judaism ( whether it be Christianity or any other incompatible belief system) does not speak for or represent the Jewish people or the Jewish faith.
ANYone born to a Jewish mother (a Jew) who abandons the religion of Judaism for Christianity, is no longer following Judaism, hence, they're a Christian.. They make themselves apostate and outside the "tribe", however, if they repent and return to God through teshuvah, they're accepted as members once again.
It is Jewish law alone, not Christianity or any other entity that determines the status of who and what is Jewish. When a Jew adopts a belief that is in conflict with the Jewish religion, the belief does NOT become a " Jewish belief" just because a Jew chooses to believe in it. THAT is the conflict Jews have with the Christians who call themselves Jews if deceptively try to present their Christian belief AS Judaism. A Jew who converts to Hare Krishna is just as apostate, but there exists no Jews for Hare Krishna or Hare Krishna Judaism evangelic groups spending millions of dollars a year in campaigns to convert secular Jews by convincing them it is a form of Judaism.
You can become a member of a tribe or nation if you meet the criteria of citizenship. And the covenant people, Klal Yisrael, remain as in the earliest days of the covenant..a nation. It hasn't changed. This type of system of laws may not be easily understood but it is not exclusive to the covenant people of the Torah, the Jews, For example, the Lakota nation has tribal procedure and law to determine who is a memberof their tribe, who is not, who is expelled and who is adopted, so does Judaism
The Jewish people are considered both a nation and a religion. Our connection is primarily one of faith (religion) through the covenant of Israel, yet membership is also conferred by birth, through matrilineal descent .One may also become a part of the nation Israel by adoption of the faith of Judaism and formal procedures of conversion.
One who converts to Judaism is considered as FULLY Jewish as one born Jewish and their children are Jews. This has been the case since the times of the Torah.
However one can be a Jew and not belong to both. One may technically be a Jew if their mother is a Jew, but apostate to the covenant of Israel and no longer considered a member of the nation if they leave it for the covenant of faith of another religion.
We are Klal Yisrael, the community of Israel, and have a shared " destiny" and history.. Many different and distinctly Jewish cultures and ethnicities have developed over the millennia in Diaspora lands. The Diaspora refers to the Jewish presence outside of Israel after the destruction of the First and Second Temple periods and the Bar Kochba revolt. Another thing many people appear to be confused. There is no ONE Jewish ethnicity, but a great many ethnicities that are distinctly Jewish. There are the Mizrahi (from the Middle East and North Africa).The Sephardi (Spanish) and the Ashkenazi, (German, Polish, Russian and other Eastern European)that are all slightly different, even within those three designations as to cultural practices and foods, but it is the faith and covenant that binds them all together as Klal Yisrael.
The Jewish nation began as a group of tribes and our connection to one another is still from the perspective of a tribal nation. ( example:as the Lakota nation has tribal procedure and law to determine who is a memberof their tribe, who is not, who is expelled and who is adopted, so does Judaism.)
One born a member of the tribal covenant nation Israel ( Jewish) may not be observant or even believe in God and they’re still a full member, a Jew. They may not be a good member or an active member but they’ve not renounced membership. That is how one may be an "atheist Jew", they still may live Jewish ethics and identify with their people, but they did not take on foreign beliefs contradictory to monotheism or Torah. Now if one born into the covenant becomes apostate to it through rejection of the covenant by adoption of another belief contradictory to the covenant, they are still be considered a Jew, but for all intents and purposes, they're not given the status of a member. According to Jewish law they're not counted in a minyan, can't be buried in a Jewish cemetery, cannot be given honors to go up to read Torah at a synagogue, and may not speak for the Jewish people. They CAN however, return without formal conversion should they so desire and then be embraced again as full members. One who has left the Jewish people for the foreign faith of another people must uindergo the steps of TESHUVAH , which means repentance and return to the God of Israel. Some groups may require that the individual also requires immersion in the mikveh before being accepted back, but they do not require the formal steps of conversion should the person wish to return
EDIT: To comment to the ABSURD notion that Hitler had any legitimacy whatsoever to determine who or what is or is not Jewish. Nazis promoted the false notion that Jews are a race. Hitler did not create that notion as it began in the late 1800's, but he did use that antisemitic propaganda and many other things against Jewish law in order to discredit and persecute Jews. Both the concept that the dogma of a contradictory religion to Judaism or the pseudo scientific ideas of antisemites to purposely insult Jewish law from used by the Nazis, could have authority to determine Jewish identity OVER the right of the laws of the people in question , reveals utter disregard and disrespect of the right of the Jewish people to self-determination according to Jewish law with regard to who is or is not a Jew.
Jewish law alone determines for the Jewish people, Jewish identity and belief.