As the Palestinians are the majority, the Jewish Israelis would become a minority in terms of citizens and votes. This is very much akin to Apartheid South Africa, where a minority ethnic group rules over the rest of the population.
Although there remains the case of 700,000 Palestinian refugees who (in the hypothetical scenario of a unified state) would tilt the balance further if allowed to return to their/their parents homes or given property as compensation for repossessed homes.