ujm, I don’t have the primary source right now, quoting from secondary sources. It appears that your assertion is not correct and RJBS continued in SCA despite all opposition and his own reservations.
RJBS sees two expressions of Jewish unity – (1) as covenantal community “You shall be unto me a kingdom of priests and a holy nation.” and
(2) based on joint historical fate “, it is a people that shall live alone”. This second one unites all Jews, religious or not, including in the eyes of our enemies. From this, it follows, as we mentioned above, (1) a need to be separate from non-religious groups/non-O groups in issues of religion and (2) a need for joint action/unity in communal issues.
now secondary analysis:
The Synagogue Council of America had been organized in 1926 by the six organizations comprising the three mainstream Reform, Conservative, and Orthodox rabbinical and congregational associations, including the RCA and Union of Orthodox Jewish Congregations of America…SCA often found itself crippled by differences among its member organizations, and survived as long as it did on the strength of a one-organizational veto, which allowed the Orthodox groups to reject any joint action (particularly one that might be perceived as straying into the “spiritual” realm) they disagreed with.
…
In 1956, the Rav’s support for the SCA came under attack both from within his community (the RCA) and from without (the Lithuanian yeshivah world). Just days before the RCA’s Halakha Commission, of which the Rav was the chair, was to meet to address a petition from the RCA’s leadership to require withdrawal from the SCA, the ultra-Orthodox Rabbinical Alliance issued a public ban on all Orthodox participation in the SCA as well as other joint rabbinical boards. Neither the Rav nor the Halakhic Commission ever formally ruled on the question, despite repeated efforts by the RCA leadership to force the issue.[11] Indeed, the issue continued to simmer, but despite a widening of the gap between the “two camps,” the RCA and UOJCA remained members of the SCA until the Rav’s death in 1993…dissolution of the SCA in 1994 simply put a punctuation mark on a completed era. With the Rav gone, it was as if the last remaining force (within the Orthodox world) trying to maintain the tension between unity and separation, to restrain the deep separatist forces at work within Orthodoxy, within the larger Jewish world, and in the wider society, was released. It was in fact a watershed. [16] What the Rav’s death marked was not so much the end of the Rav’s influence, but the end of the milieu in which Conservative as well as Orthodox rabbis (and to some extent even Reform rabbis) came from (and in some cases adhered to) traditional roots and perspectives that made debates among them still possible.
[9] Rabbi Walter Wurtzburger, in an essay on the Rav’s life and writings, writes unequivocally that the Rav strongly supported continuation of RCA and UOJCA participation in the SCA, recounting that he and the Rav, along with Rabbi Klavan had strategized how to keep the SCA status quo from falling apart. See, “Rabbi Joseph B. Soloveitchik as Posek of Post-Modern Orthodoxy,” in Angel, Marc D., Exploring the Thought of Rabbi Joseph B. Soloveitchik, at 14 (1997).