Debates about democracy are purely hypothetical, because it does not meaningfully exist in any of the countries which claim to implement it. When I talk about democratization of power, I am not talking about a political process focusing on governments; I am talking about a strategy of activism to impose accountability on the entities which exert real control over society.
That said, democratically determining what is Halaal and what is Haraam is kufr; but allowing the population to have a say in who will manage the society is certainly not kufr.