Boas's agenda remained consistent over his entire career, and it's not an agenda he picked up in America. Boas was born in Germany, studied anthropology in Germany, brought his fully-formed worldview with him from Germany, and continued to identify with Germany throughout his life.
This paper (Leonard Glick, Types Distinct from Our Own: Franz Boas on Jewish Identity and Assimilation. American Anthropologist, 84: 545–565.) provides some background on the world Boas was born into (including discussion of Jewish emancipation, the German reaction, the 1848 revolutions, etc.) and how this background affected Boas.
For a problem of such magnitude, he continued, there could be only one solution: “Israel must renounce its ambition to become the master of Germany.” The Jews should accept at once the inescapable necessity that their influence in German life be curbed and abridged through strict quotas in every public sector, and through reorganization of the nation’s economic structure. “Either we succeed in this,” he concluded, “and Germany will rise again, or the cancer from which we suffer will spread further. In that event our whole future is threatened and the German spirit will become Judaized” (ibid.:287). The impact of this speech on Berlin political life was “extraordinary,” says Massing, and for the next five or six years the so-called Berlin movement, led by Stoecker and with anti-Jewish agitation as its definitive characteristic, “kept the capital in a turmoil” (ibid.:30; Boehlich 1965).Nor was it "liberal WASPs" Boas primarily affiliated himself with in America.
In 1881 Stoecker was elected to the Reichstag as representative for Siegen, the constituency immediately adjacent to Minden, and retained this position for many years. He was also by then representative for Minden to the Prussian Diet and is said by one German historian to have been “at that time one of the most popular men in Minden- Ravensberg” (Herzig 1973:125; Pulzer 1964:99). His opponent in the Reichstag election was Rudolf Virchow, the distinguished physical anthropologist and progressive politician with whom Boas soon afterward established close ties. Stoecker distributed an election-eve pamphlet describing Virchow as a defender of Jewish usurers. Moreover, he continued, the Progressives (left liberals) were calling Virchow “the representative of culture,” but “I do not want any culture that is not Germanic and Christian” (Massing 1949:41). [. . .]
It was in this troubled social environment that Franz Boas grew to young adulthood. Clyde Kluckhohn and Olaf Prufer, writing on his “formative years,” have something to say about the intellectual life of the period but make no mention of Volkish ideology. They do note that anti-Semitism was an important problem for Boas: “The letters from Kiel,” they remark, “are particularly full of accounts of unpleasant activities among the student body, and of gross personal behavior” (1959:10-11). Commenting on the same period, A. L. Kroeber says that the “non-intellectual aspects” of Boas’s university life “may be presumed to have been warm and rich,” but he also notes that Boas left with “several deep facial scars from sabre cuts received in duelling.” He then refers, somewhat ambiguously, to Boas’s self-identification as being of the “Mosaic confession” and to a story about a fight and duel following an anti-Semitic insult (1943:7-8). 5 Stocking states explicitly that the duels were “fought over anti-Semitic remarks” (1979:33).
His immediate solution to the question of religious identification, to the extent that he accepted this as a question, was to become a member of the Society for Ethical Culture, founded in New York City by Felix Adler, an educator, social activist, and later professor of political and social ethics at Columbia. Adler was the son of the rabbi of the most prestigious Reform congregation in the country, Temple Emanu-El of New York. It was anticipated that he would succeed his father in the same pulpit, but at age 22 he delivered a guest sermon, entitled “The Judaism of the Future,” which permanently eliminated that prospect. Judaism, along with all other formal creeds, was on the verge of extinction, he declared, and the only proper course was abandonment of religious particularism in favor of a humanistic faith embracing all humanity: “... we discard the narrow spirit of exclusion, and loudly proclaim that Judaism was not given to the Jews alone, but that its destiny is to embrace in one great moral state the whole family of men…” (Radest 1969: 17; emphasis in original). This was, in fact, wholly within the spirit of Reform Judaism, although Adler carried the argument a step further by inviting eve[r]yone to join. In his lecture inaugurating the Ethical Culture movement, delivered in 1876, Adler proposed “to entirely exclude prayer and every form of ritual,” and declared his primary allegiance to “freedom of thought” as the “sacred right of every individual man” (ibid. :27 -28).
The organization prospered and achieved something of a reputation for service in the interests of social reform and humanitarian ideals. The membership was heavily and probably predominantly composed of cultivated German Jews, for whom it gave organizational legitimation to the very same values that Boas summarized as “the ideals of the revolution of 1848,” and it is quite apparent why it appealed to him. 8 Although he does not appear to have been deeply engaged with the Society’s program, he did travel to London in 1911 to deliver a lecture on “Instability of Human Types” at a Universal Races Congress, sponsored by the Society, which brought together Asians, Africans, and Europeans for what may have been the first such effort to achieve genuine cross-cultural exchange on a formal level (Radest 1969:93-94).