Often it's the shadow of violence that is most effective. A peaceful protest, that is safe enough for families etc is perfect for snowballing. Focused action and the threat of counter violence keeps the government in check.

Too violent, and the support collapsed, letting the police simply overwhelm it. Too passive, and the whole thing can be ignored.

The Irish troubles are a good example. Protests and marches showed popular support. While the Sinn Fein party provided a political face. The IRA then made sure that proper attention was paid. All 3 were required to achieve their goals.

it took an entire fucking war to end slavery in the United States.

Well... how's that going?

Now we are debt slaves instead. Success.