Is there a philosophical justification for democracy? It seems that it would have to be an argument from self-interest, but if we ask, "Whose self-interest?" then it would seem that a democracy isn't the best form of government for certain minority groups (e.g., a theocracy might be more in line with the interests of religious fundamentalists). And what if democracies are even downright harmful to, e.g., the elite?
Also, a somewhat related question: is there a philosophical justification for taking from the rich and giving to the poor (which it seems is what socialism prescribes)? This question is 'somewhat related' to the previous question in that even if a democracy does benefit all, it certainly deprives certain groups of advantages they might otherwise have, and so, given a history, it cannot actually benefit all equally.
Democracy is a form of government in which the sovereign power is vested in the majority, rather than being vested in a smaller group, such as an aristocracy, or in one person, e.g., a monarchy. A democracy does not necessarily seek to benefit all, indeed Mill talks about the tyrrany of the majority. So a democracy must be limited in some way that prevents such tyranny. The United States seeks to limit democracy by means of the Constitution. I would prefer to say that a democracy must be limited by morality. Given that kind of limitation, a democracy decides among the morally acceptable alternatives by the votes of the majority, either directly or indirectly. One justification of this kind of democracy is that since all of the alternatives are morally acceptable, then it seems appropriate that the decision among these morally acceptable alternatives be made by a majority of the people, rather than by some smaller subclass.