That quote isn’t saying “we should go start some violence for a bit of fun”.

It’s talking about the exact revolutions that were ongoing during that period (see the section on 1840s geopolitics), and noting that the ongoing revolutions give an opportunity for citizen centred political system - ie a democracy.

ACAB isn’t some international stance the left takes. It’s a reaction to the frequently racist, violent and corrupt policing specifically in the USA. And it certainly doesn’t mean there should be no law enforcement whatsoever - you’d be extremely hard pressed to find anybody who would take that stance.

Violence always begets more violence, there is literally no exception

Counterexamples: the British suffragette movement (which was notably extraordinarily violent, despite its common modern image as a quiet, polite disagreement), the American civil war, the Swedish coup of 1809, the Ukrainian defensive resistance in the ongoing Russo-Ukrainian war.

Gandhi was a fantastic and principled man, and had an enormous impact. But, whether or not he liked it, violence was absolutely a part of the end of British colonial rule, and would have been even if every revolutionary was exclusively nonviolent, because the violence by the British was not conditional on violence by the Indians.

But all of this is separate to the key point - regardless of whether one considers it an effective method of revolution, violence isn’t the aim of a communist system, and it’s use is only considered acceptable in a scenario where that is not the current system, and when it would be the only possible method to overthrow that system.

Edit: as an aside, even Gandhi accepted that violence can be necessary:

Even though Gandhi considered non-violence to be “infinitely superior to violence”, he preferred violence to cowardice. He added that he “would rather have India resort to arms in order to defend her honor than that she should in a cowardly manner become or remain a helpless witness to her own dishonor”