Those who really have power in this society tolerate democracy only so long as it doesn't infringe on their power. If, through the parliamentary system, we ever began to expropriate industry, then the people who have wealth and power would destroy the parliamentary system. In this respect there probably wouldn't be any way within the system. But any revolutionary I've ever heard of must prefer peaceful non-violent means if these are possible. But it's rarely been possible because of the resistance by those who want to preserve their privileges.