Andrew Walder makes a pretty good case that the worst violence of the Cultural Revolution was perpetrated by the Military in their bid to stabilize the situation and suppress mass mobilization. The campaign to "cleanse class ranks" which followed also devastated the Left Wing -
The violence committed PMA in suppressing rebels was 4 to 5 times greater than that committed during Red Guard or other factional violence. Many assume that the army brought stability to a hopelessly chaotic situation but it looks like they only made it bloodier -
In many places factional warfare intensified with the local PLA units' intervention on behalf of the appointed "Left". This "Left" was not defined, and so the PLA labeled anyone who opposed intervention as "conservative", regardless of ideological affiliation or social background
This inability to define the left by clear criteria put the PLA in the awkward situation of supporting conservative groups and rebel groups all over the country, thereby harming the revolutionary Left's ability to make even gains or consolidate what they had - & this brings us ..
Back to the violence, which killed hundreds of thousands of student and worker rebels, and dealt the mass movement a blow from which it would not recover. The PLA restored a semblance of "order", but at the cost of crushing the atmosphere of mass mobilization of the GPCR.
Popular portrayals of the GPCR depict the violence of a minority of Red Guards or factional warfare, but say silent about crushing the mass movement. This is bc it is the idea of mass mobilization is itself seen as terror, while law and order, no matter how brutal, is valorized.
Sorry this was kinda rambling but feel free to pitch in your thoughts - I came across as painting the PLA with a broad brush, and I feel the question of their role is much more nuanced, but they also added fuel to the crisis and contributed in some profoundly unhelpful ways.