YB, qwerty613 and ZSK:
Rav Elchonon Wasserman stated clearly in Kovetz Maamarim that Zionism is idolatry and that “Religious Zionism” is idolatry mixed with some (true) religion. Other gedolim did as well.
As to why Zionism is heresy and idolatry, that is simple. Ain od milvado and Toras Hashem Temimah. If you add anything to the Torah (like “Religious Zionism”), then you are by definition detracting from the Torah, which is heretical. And if you believe that anything usurps/replaces any part of G-d’s power, then you are necessarily making that into an idol. You could even make yourself into an idol.
So, for starters:
The Torah states that Hashem guarantees that the Jewish people will last forever. LiHavdil, the heretical Zionists, in the very beginning of their “Jerusalem Platform” of their core idolatrous ideology of Zionism, state (some lies omitted from the quote for brevity) “Zionism…views a Jewish, Zionist, democratic and secure State of Israel to be the expression of the common responsibility of the Jewish people for its continuity and future.”
In other words, according to the Zionists, it is not G-d, but the Zionist “State” that guarantees the “continuity and future” of “the Jewish people”.