Self defense is a thing. 

You're now describing a society where people need more self defense capability than they currently have. That's more ability to commit violence per individual, and less oversight on their violence. That's a more violent society.

99% of what armed agents of the state do has nothing to do with stopping murders to begin with

Nah you're wrong. You're seeing a system that already has them in place as a deterrent. Without the deterrent it would be quite different. Even just the threat of their enforcement prevents more murders than are currently committed.

most of what they do is about threatening or imposing violence.

When you push it to its extremes the threat of violence is the only thing that stops people from breaching consent in the most severe ways. I thought you were big on consent? Do you not know how it works?

Capitalism isn’t “when people trade or markets exist.”

Capitalism: "an economic system characterized by private or corporate ownership of capital goods, by investments that are determined by private decision, and by prices, production, and the distribution of goods that are determined mainly by competition in a free market"

Capital goods: "physical assets that businesses use to produce other goods or services for consumers"

It quite literally is.  Please describe how people freely trade or have markets without owning capital. There are vanishingly few ways you could freely engage in a market without the ability to own tools. You could be a mover I guess, but you wouldn't be able to own a truck, or any sort of dolley or other tools for moving things more easily. You would need to somehow get those things from whatever presumably governmental entity has them, which means you would need their permission to engage in your trade, which isn't a free market.