You can’t make halachic decisions concerning social tenets from the Torah or Gemora. Slavery is sanctioned by the Torah yet nobody in their right mind would say that today slavery is OK. There was no concelt of democracy in those days anywhere in the world. And there is no way of knowing that when moshiach comes, what type of government we will have. Of course it will be in strict adherence to halacha and Torah philosophy. But until moshiach does come, democracy is the way to go.
