They put on uniforms that are invariably too tight or too baggy, sign out their gear and guns. Then, scrambling onto military vehicles, 70,000 reservists—women and men—join the young conscripts of what is proportionally the world's largest citizen army. They all know that some of them will return maimed or not at all.

And yet, without hesitation or (for the most part) complaint, proudly responding to the call-up, Israelis stand ready to defend their nation. They risk their lives for an idea. The idea is Zionism. It is the belief that the Jewish people should have their own sovereign state in the Land of Israel. Though founded less than 150 years ago, the Zionist movement sprung from a 4,000-year-long bond between the Jewish people and its historic homeland, an attachment sustained throughout 20 centuries of exile.

This is why Zionism achieved its goals and remains relevant and rigorous today. It is why citizens of Israel—the state that Zionism created—willingly take up arms. They believe their idea is worth fighting for. Yet Zionism, arguably more than any other contemporary ideology, is demonized. "All Zionists are legitimate targets everywhere in the world!" declared a banner recently paraded by anti-Israel protesters in Denmark.

"Dogs are allowed in this establishment but Zionists are not under any circumstances," warned a sign in the window of a Belgian cafe. A Jewish demonstrator in Iceland was accosted and told, "You Zionist pig, I'm going to behead you." In certain academic and media circles, Zionism is synonymous with colonialism and imperialism.

Critics on the radical right and left have likened it to racism or, worse, Nazism. And that is in the West. In the Middle East, Zionism is the ultimate abomination—the product of a Holocaust that many in the region deny ever happened while maintaining nevertheless that the Zionists deserved it.