what you say doesn't change the fact that there'd be more civil wars/fighting in an anarchistic society.
I don't believe this would be the case. Most of the wars of the past century, at least, would have been eliminated if the subjects could secede. One reason I am pro-anarchy is that I am anti-war.
i'm not sure how that changes things. if you are suggesting that the entire world should transition to anarchist systems, which we have no example of, then there would absolutely be power vaccums, which would lead to war.
Is there some reason people can't defend themselves against oppressors without having to oppress others to do it?
Yes - war requires cash so to win, you have to use force to raise the cash. Voluntary donations are OK but the real money is in protection rackets and kidnapping. Or at least that's how it worked in Ireland when I was growing up. From what I see in places like Syria and Iraq, nothing has changed.
it's moreso resources than cash, but i overall agree. you need at least some sort of competitive advantage to beat someone, and resources are a main component of that.
I'll start off with a few house-state problems:
1. Roads. The roads are built and maintained by nation-states, and house-states will, by necessity, use them. Since the house-state doesn't pay taxes to the country-state, the country-state now has to devise an awkward & costly toll system. And an enforcement system, different from an existing enforcement system, to enforce the laws regarding "home-staters." For instance, i think i make an awesome drunk driver, and as a free individual, i don't wish to be penalized for simply being a potential road hazard. As long as i don't do any actual harm, i should be free to do as i choose, amiright? Then a State Thug pulls me over & wants to penalize me. The problems start.
You can see endless similar problems sprouting up. The reason large societies are able to function at all is the universality of standards. English, for instance, is far from being an ideal language. But if everyone talked in their own, custom tongue, communication would be impossible.
Sorry for veering of on seemingly disjointed tangents, but i see so many problems. Sort of like granting every cell in your body complete autonomy, and expecting to stay alive. And even get better for it

that's the problem.. who will invest in infrastructure? the one who does that will have all the power because they control access to trade. if say i am a large supplier of apples.. all i'd need to do is provide some money and maybe allegiance to whoever the fuck owns the roads, and they will ensure my transporter will be safely escorted. that creates an advantage for me over my competitors. i will gain more money and power, and continue the process until i'm filthy rich and everyone else is poor. they are then economically disarmed.
let me reiterate.. herein lies my point: government is a problem, but
the nature of man is THE problem. if you remove government, you still have the nature of man.. which is to dominate others.