If both Zionism and Apartheid as political ideologies favoured one group of people over other inhabitants why is it okay to disparage one and not the other ?

Apartheid is one of the crimes committed by Zionism, rather than a general descriptor as it is too inadequate a designation to account for every manifestation of Zionist settler colonialism. The solution does not only lie in a civil rights movement for equality or the mere incorporation of the West Bank or Gaza Strip into the Israeli state. After all, even if Israel stopped practicing Apartheid, without true decolonization and the right of return, the Palestinian struggle for liberation would be incomplete. The Palestinian cause is a cause for decolonization and freedom, not for acquiring privileges in a colonial state. As to why it is ok to disparage one but not the other? Simply because Big momma US protects Israel. Any legitimate criticism of the warcrimes and oppression done by Israel’s apartheid towards Palestinians is faced with the false magic label of antisemitism to shut the whole conversation down. I do not think this will last.
A Palestinian woman holds a poster during a solidarity rally in London. Photo courtesy of ZUMA Press.