I will attempt to re-word my post so it gets allowed through.
HaKatan, you say Rabbeinu Tam did not abandon his mesorah from Rashi.
As is well known, there is a difference of opinion regarding tefillin between Rashi and Rabbeinu Tam. Rabbeinu Tam disagreed with the mesorah he had from his grandfather, and changed the order of the parshiyos in his tefillin.
Rashi also held that we should put our mezuzos on the doorpost in a vertical position. Rabbeinu Tam disagreed, and held it should be horizontal.
In both these cases, Rabbeinu Tam argued on the mesorah of his grandfather.
In the case of Israel and Zionism, there is more reason to allow arguments. R’ YB Soloveitchik’s father passed away before the state of Israel was founded. It’s very possible he would have changed his views after the founding. Additionally, while he may have said non-religious Zionism was wrong, he did maintain a warm relationship with religious Zionists (particularly the Mizrachi movement). It’s possible he was in favor of religious Zionism.
In any case, my Rav is a student of R’ Herschel Schachter shlita, who was a student of R’ YB Soloveitchik zt”l. R’ Soloveitchik was a member of the Moetzes of Agudas Yisroel, and was held in high regard by other Rabbonim. There is absolutely nothing wrong with following his halachic opinions.