Nonviolence is better than violence because nonviolent protesters have have moral high ground. Nonviolent protesters, if harassed or killed are martyrs. Violent protest would be sinking to the level of their oppressors and give them a reason to strike back, continuing a cycle of killing that could last forever. Whereas if protesters are nonviolent they are better than the opposition. (lots of religions have roots in the idea of nonviolence, like satiagraha in hinduism and quakerism has similar practices)