We are not talking about oil rich countries or even a Islamic Union where a pledge that all natural resources belong to all Muslims not only to saudis or iranians or malaysians. However for the modern nation state currently we need to think out a tax system to save lives and reduce sufferings. Zakat by itself without wealth and resource distribution wont fulfill the needs. Only the concept that Zakat + wealth/resource belongs to all needy Muslims is the only solution to avoid taxation. Until then we have to tax well-off people or avoid that immoral act and let people die/suffer (another immoral act). Choose which one you prefer.