The Israelis have argued that a one-state solution won’t work since Arabs and Jews hate each other. Remember that in a single state, based on the original “Palestine/Eretz Yisrael” borders, Arabs would be a clear majority. The Arab position is that the fight isn’t about borders or settlements, but over partition. They want a single state from the desert to the sea.
If a significant number of Jews support the Arab position, and if the Arabs can point to Jewish communities living under their rule with Palestinian passports, it would totally undermine the Israeli’s claims. A simple majority in the United Nations could repeal the partition resolution and call for an internationally supervised election to establish a democratic government.
If the zionists manage to force all the hareidim (including those supporting Shas, Agudah and Degel ha-Torah) to become anti-zionists (similar to Satmar, Toldos Aharon, Neturei Karta, Eidah hareidis), and the Arabs exploit this by offering to allow hareidim to live in their territory (a return to the pre-1914 status quo) this would seriously undermine Israel’s right to exist.
Israel was created by goyim (and assimilated Jews) as a place to be a haven for persecuted Jews. If the most Jewish part of the population is supporting a democratic non-zionist solution, it will undermine the zionists and lead to the end of their dream of a secular state. Remember, hareidim have no problems being an autonomous minority under Islamic law.