Zionism was originally an idealistic thought and evolved into something unrecognisable today. It was supported by most people across the world before. Zionism is inspired by nationalism, as was Nazism. If we bring your logic to its ultimate conclusion, then it goes to the circular questioning as to why is nationalism not been banned, despite causing so much harm and atrocity? Why is African nationalism not banned? Or Indian nationalism? Or Ukrainian nationalism? Even the history of nationalism has started with the best intentions. As had happened with most ideologies, however, they don't end well. I think even the the mildest form of nationalism will eventually end up extreme. Nationalism is making a pact with the devil and expecting the due will never come. That is what happened on German nationalism leading to Nazism, and Israeli nationalism leading to Zionism. And soon, American nationalism leading to MAGA nationalism.