For argument's sake let's consider me normal. Also for the sake of argument let's assume I will _not_ get hostile ;-)
1) It appears that there is a reduction in violence when one entity (usually the state) achieves a monopoly on law and force. This is because a) individuals when wronged (victims) have an avenue of redress and no longer can take matters into their own hands and perpetuate cycles of violence and b) if an individual trangresses against another's person or property they can be assured of at least some response from a well-resourced state rather than a weak individual. That's the theory anyway but it appears borne out by the stats. I would direct you to read the very excellent Better Angels of Our Natures[1] by Stephen Pinker which changed my thinking on this issue. There's a ton of convincing researched data to back up my position contained within its pages.
2) With 'funded by theft' you of course mean taxation. This is probably where you encounter most hostility. Most people will obviously prefer less taxes (for them) as opposed to more because they'll have more money in their pocket, right? Never mind the fact that barring corruption their taxes go into a common pool to be used for public services and infrastructure and that a higher rate of taxation might improve their lot -- witness the oft touted Scandinavian model. Now to the logical conclusion of this train of thought is, "why not desire zero taxes!" (ie. less and less and less taxes until you reach zero.) You could argue for this. It's quite _another_ thing to argue that taxation is thus theft. That, frankly, makes you sound like an extremist and usually signifies that arguing with you will be a futile experience. Like it or not you live in a society that has public services and infrastructure, money is a consensual public tool -- you gain enormous benefit from this system, you wouldn't even have money to steal if there wasn't the agreement that we'll use this money thing is a exchange mechanism in the first place. I'll be honest, this position exasperates me -- I see it often on HN but rarely respond because what's the point, you won't change your mind. But I'm putting it out there this time, I _strongly_ disagree with your position and I would _not_ like to live in the society you envisage. Over to you :)
[1] http://www.amazon.co.uk/The-Better-Angels-Our-Nature/dp/0141...
Does the data you're hinting at include wars? Does it attempt to control for other variables which may be somewhat orthogonal to the existence of a state, like technology, medicine, wealth, types of weaponry in existence, etc.?
http://en.wikipedia.org/wiki/List_of_wars_and_anthropogenic_...
and sort by Percentage of the world population. Five conflicts: Mongol conquests, Late Yuan warfare and transition to Ming Dynasty, An Lushan Rebellion, Qing dynasty conquest of the Ming Dynasty, Conquests of Timur-e-Lang all were more bloody as far as we can tell (per capita) than WW2.
It does not attempt to control for other variables. This is a deeply complex caveat. It is not like for like because societies move on in terms of, as you say, technology and so on. Our medicine is better now and our weapons are more lethal.
Violence is taken to include person on person violence, state violence towards persons and state on state violence (wars). Read the book! Hope that helps :)
I mean, we all see what can happen when a police state goes bad so that prompts some to imagine a utopian world without the 'evil' cops but unfortunately we had that world in the past and it was, in fact, worse. This is not comparing like with like though. It would be difficult to definitively know without, I think, accurate computational modeling of societies and that's a toughie, I don't know if anyone has tried that. Stephen Pinker does provide data on societies that haven't integrated into the modern world (hint: more per capita violence than our own, including the US which is far more violent than any other developed country) and also there is archaeological and historical evidence from societies of the past (seems to indicate they were more violent as well: homicide, torture, theft, rape, ...)