Any sufficiently large gang, left well enough alone for long enough, will become the de facto state.

Again this is kind of non sequitur. No one argued that they wouldn't. States are definitionally just gangs that have been legitimized.

Your own local anarchist conclave may all be friendly and would never do such a thing to their neighbors. But if the next one down the road decides they need your land and resources, and if they outnumber and outgun you, then you're just done for. No one will come to help defend you. No one will arrive to mete out vengeance afterward.

And? None of these are gotchas of any sort. Even that case is still preferable to the state doing it. If the state does it does that make it better/more acceptable. And at that point wouldn't that group be a burgeoning state anyway? This is why anarchist are strong advocates of arming the populace.

The state holding an implied monopoly of violence is what enables said state to enact their atrocities, but is also what prevents smaller groups from falling into the same trap.

Smaller groups are capable of less total violence at scale. That's like saying, more violence is justified, otherwise we would effectively have less violence. It doesn't make the sense you seem to think.

Oh and there is also a huge difference between the state acknowledging that it is at War for territory. And not being at war for territory. In the United States my people are constantly at war with the state to preserve what little territory we've been left. Let alone get back what the state stole. But it's okay because the state did it therefore it's okay. Otherwise some roving gang might have gotten much smaller section of it. And that would be so much worse than losing nearly all of it as we did.

And no community is an island. You keep mentioning "my community" as if that is all there is. Or that having neighbors and allies is impossible. All you arguments realistically just boil down to "we need the state, or else the state". Classic circular reasoning.