In all brilliant theories that have ever been conceived by respectable philosophers or thinkers lie excellent critiques of the nature of structures and institutions and draw our attention astutely to certain natures of man that have been left out by those structures and institutions. Plato drew our attention towards the lack of objective justice when "might is right" and believed that man lives best when he is well placed in the divine order dictated by objective truth and justice. Hobbes raised very important concerns about the necessity of peace in order to merely survive as dignified beings, and so touches on the need for a 'Leviathan' to prevent man from falling into a state of anarchy. Locke criticized the stifling nature of the state in preventing us from being free, independent and equal beings. Marx attacked the alienating nature of industrialization and capitalism, drawing our attention towards the fact that we are, ultimately, social beings.
The inevitable flaw that accompanies every brilliant theory, though, is in its attempt to rationally propose a strategy based on its critique for man to follow and attain some form of ideal end. Even worse is our glaring incapability as human beings to carry out grand strategies, because an ideal end requires sacrifice and the tendency for self-interest can never be completely pushed aside. The greatest 'flaw', if I were to indulge in a loaded word, of our nature is in the tendency for some men to even use the proposed theory to their self-serving advantage. We've seen this play out with all the thinkers I had mentioned. Their good intentions eventually provided the legitimacy for various forms of tyranny to occur, such as totalitarianism, fascism and rampant corporatization, to name a few.
Were we never meant to achieve ideal ends? Are utopian goals an evil in itself? Why has there never been a theory that can work perfectly? It seems like, as beings torn between knowing and not knowing, and having intelligence but being of limited perceptibility, the best of us are capable of providing sobering accounts of how drastically wrong we were and illuminating what we are as human beings, but are never quite capable of proposing a game plan that can cover all the loopholes that our nature can exploit.
If there was a theory I would consider 'most right' though, it would reside among the circles of Socrates, Plato and Aristotle, and later St Thomas Aquinas. They were primarily concerned with the 'shaping of the soul' from young. What this essentially means is that people should be taught virtues and should be allowed to interact based on shared morals that were derived from objective principles of truth and justice, rather than on rules and laws. When the sensibilities of society are already well established, a population made up of enlightened and compassionate citizens should fare better than any other population that has to depend on rules and regulations to correct evils.
The problem with this plan, of course, is its immense difficulty in implementation, far greater than any other easier-way-out ideology that exists for states to utilize today. And even then, the concept of states and sovereignty itself is a recent and proximate phenomenon, borne out of Hobbesian and Machiavellian prescriptions.