And when did exactly a bunch of protesters *alone* manage to tear down "the system" that had not already been torn down by a war (e.g. Russia after 1st world war) or foreign occupation (e.g. China after 2nd world war) or do so without a massive help from foreign governments (e.g. Vietnam aided by the USSR and China)? In other words, I am yet to see a single case of an even moderately successful "tearing down the system" by a movement from-below not preceded by the destruction of the local institutions by a cataclysmic event and not accompanied by a substantial assistance from another state or a ruling elite.
I think that leftist fantasies about ideologically pure revolution from below tearing down the existing institutions is at best a bunch of romantic crap, a sour-grapes rationalization of its own irrelevance, and at worst a defeatist ideology that prevents from engaging in a politically meaningful action.
For the starter, I suggest reading _Strategy of Social Protest_ by William Gamson, which examines various social movement in the US history and concludes that a success means cooperation and cooptation by the existing institutional structure - none of these movements came even remotely close to tearing down "the system" or even builiding a parallel power structure.
Besides, "ideologically pure" parallel institutions dreamed of by some on the US left smack of the utopian socialism rightfully derided by Marx.
PS. As far "ideological purity" is concerned, there is an excellent article on the Pacifica debacle in the latest issue of The Nation. In short, the debacle is caused for th emost part by wannable intellectual celebrities, who got stuck in the 1960s, rationalize their national irrelevance as "community broadcasting" and protecting their intellectual truf under the guise of "free speech." Sounds like another case of the sectarian US left more concerned about their own celebrity status in a marginal but "ideologically pure" (read: uncritically following the line set by the leader) cult than political efficacy and reaching mass audiences.
wojtek