There is a distinct difference between progressive and reactionary violence

The rule of "law and order" takes constant systemic violence to upkeep, to protect the ruling class, their private (not personal!) property and interests.

This violence of the ruling classes is normalised, even legalized/codified in law. Standing up against it, however, and enacting systemic change is branded by their lackeys as "terrorism" or "violent chaos".

Class struggle is a constant fight of one class to oppress another. Currently in most of the world, the exploitative classes oppress the exploited ones. For society to progress, the exploited must suppress the exploiters.
(Or for the expropriators to be expropriated as Marx put it. But that's just the same in fancy)

After all

One person's terrorist is another one's partisan

Mao put it quite well, which is why all following quotes are from him
(btw jsyk: quoting someone on a specific issues doesn't mean supporting their views in general/every other aspect)

"War is the continuation of politics." In this sense, war is politics and war itself is a political action; since ancient times there has never been a war that did not have a political character.... However, war has its own particular characteristics and in this sense, it cannot be equated with politics in general. "War is the continuation of politics by other . . . means." When politics develops to a certain stage beyond which it cannot proceed by the usual means, war breaks out to sweep the obstacles from the way.... When the obstacle is removed and our political aim attained the war will stop. Nevertheless, if the obstacle is not completely swept away, the war will have to continue until the aim is fully accomplished.... It can therefore be said that politics is war without bloodshed while war is politics with bloodshed. - "On Protracted War" (May 1938), Selected Works, Vol. II, pp. 152-53 *

Revolutions and revolutionary wars are inevitable in class society, and without them it is impossible to accomplish any leap in social development and to overthrow the reactionary ruling classes and therefore impossible for the people to win political power. - "On Contradiction" (August1937), Selected Works, Vol. I, p. 344.*

War is the highest form of struggle for resolving contradictions, when they have developed to a certain stage, between classes, nations, states, or political groups, and it has existed ever since the emergence of private property and of classes. - "Problems of Strategy in China's Revolutionary War" (December 1936), Selected Works, Vol. I, p. 180.

This is why only after the abolition of classes, private property and states (ie. communism), will the contradictions, which are the root cause of virtually all large scale violence, be resolved.

Which in turn is why:

We are advocates of the abolition of war, we do not want war; but war can only be abolished through war, and in order to get rid of the gun it is necessary to take up the gun. - "Problems of War and Strategy" (November 6, 1938), Selected Works, Vol. II, p. 225.