The concept both of social violence and violent maintainance of the status quo through cops, imperialism, etc. are helpful. So is a simple trolley-problem framing. The revolutionary socialist does not like violence (or in any case shouldn't), but they see it as necessary for the purpose of stopping the violence that is continuously enacted by the ruling class. If cops were beating someone to death for shits and giggles, would it be wrong to brick them or wrong to not brick them and let their victim suffer and die?