At a certain point; when democratic processes appear to be undermined and controlled by undemocratic power structures and the elected government observably caters to a minuscule segment of the population, and the avenues of recourse appear to be corrupted; people rather naturally become alienated from the political system, and even tend to support its downfall. When things have reached this degree of estrangement and discontentment, it might be constructive to begin directing your efforts not to the dismantling or toppling of the government and other institutions of power, but rather to building a parallel system.
The same applies, of course, to formally undemocratic societies.