Violence is generally counterproductive to any goals that a revolutionary group has. Revolutionaries fighting for economic equality or freedom of their people lose respect and sympathy from the wider community when they resort to violence. Consider our own country: Martin Luther King Jr. was a man who fought justly and peacefully for the civil rights of African Americans, and he is remembered as a great leader who did great things for our country. Then consider Malcolm X, another civil rights leader preaching a very different approach. He is remembered much more controversially and is generally considered to be much less effective than Martin Luther King.
That said, when a group is pushed down long enough, eventually they will rise. And if they are deprived of enough rights, if their voices are ignored, then they will see no option but to react violently. When governments brutally repress their people, sometimes violence is the only way to create any sort of statement.
"And the great owners, who must lose their land in an upheaval, the great owners with access to history, with eyes to read history and to know the great fact: when property accumulates in too few hands it is taken away. And that companion fact: when a majority of the people are hungry and cold they will take by force what they need. And the little screaming fact that sounds through all history: repression works only to strengthen and knit the repressed." - The Grapes of Wrath-