This has two interesting issues right in the first sentence.
Most I know are generally opposed to violence, with some exceptions allowed for . . .
The idea of violence being a categorical bad with "exceptions" where it is permissible due to some carveout is deontological reasoning that has no place in a materialist assessment. Violence has severe downsides that mean that it should be minimized, but the degree to which it can be minimized without some greater downside (particularly violence from another party) coming about or continuing is something that varies situation to situation. Sometimes violence isn't useful, so its introduction only has downsides. Sometimes it is one of several options that are all reasonably arguable. Sometimes it is clearly the only option to prevent a much greater violence.
with some exceptions allowed for any revolution or class struggle.
[Setting aside the word "any" there] What do you think these words, "revolution" and "class struggle," mean?
Do you think a revolution -- or whatever makes it worthwhile, since that surely is not revolution for its own sake -- is something that is achieved eternally after fighting for a few years, or something that must be continuously protected from forces trying to sabotage you from all angles?
Do you think that "class struggle" is something where you hang a few capitalists, wash your hands of the blood, and then kick back and relax? Or is it a continuous process of trying to resolve the contradictions in society on a basis that follows the broad democratic consensus of the working class? There are going to be workers who are bought off by capital, or radicalized by cults it supports, or any number of other things, and these workers will then seek to destroy your socialist state while Trotskyists in the North Atlantic cheer them on. Do you let this small group -- typically representing foreign powers or the most monstrous of infections you have let fester in your own society -- dictate the destruction of the socialist state even as the majority wishes for it to be preserved?
I am reminded of a quote from Michael Parenti in one of his lectures:
Mercenary armies, destruction of the productive facilities of the society, more invasion, more sabotage, economic boycott, economic embargo, monetary embargo, technological embargo. These have distorting effects upon a society…
When the Sandinistas came to power in Nicaragua ten years ago, filled with ideals and hopes for their nation and their people, they discovered a very awful thing, and it wasn’t about themselves, even though they had to do it to themselves. It was about that capitalist encirclement. They discovered that they needed a secret police. They discovered that they needed a security police because all around them, coming in from two borders and within their own society, were acts of sabotage, espionage, attack, mercenary invasion and the like, and they understood that if the revolution was going to survive, it would have to build up instruments of state power, instruments of coercion even, and these instruments, by the way, can make mistakes, and these instruments can not only make mistakes. They can commit some serious crimes, although in Nicaragua the impressive record is how few crimes there were, given the utterly dire conditions they were under.
(It's worth noting that "secret police," as far as I can tell, is what you call the "intelligence agency" of a country hostile to the US)
This is all glossing over the fact that the violence by the CPC was not directed at the civilian students -- who it gave plenty of warning to evacuate -- but to the militants who had already immolated and lynched unarmed soldiers who were supervising the protests.
Unfortunately for the CPC, there was also a group of students (a tiny subset of the larger movement) being lead by people who were either religious zealots (Christians, in this case) or bought off and were consciously making the group stand its ground in hopes that they would be caught in the crossfire, which happened in some cases. We know this in part because one of those leaders very helpfully told us as much in an interview. She did escape and had a fruitful career in the US working with various Republican think tanks and the like. I assume that the recruitment vector was her being Christian, but I don't know.
Anyway, that's just a very basic overview because I thought I shouldn't leave your actual claims uncontested, but I mostly wrote this comment for the first couple of paragraphs.