Your basic intermediate decision sciences text book teaches constrained optimization as the basic tool. For economics, however, optimization is only the first step--then you have to compute equilibrium. I'm not sure we can say that security is really about economics if we don't take the broader, social welfare analysis approach.

Well, and this confusion as to what economics is was the basic thrust of my uncertainty on the aphorism.

I think the view of the econmists is that everything is about economics. In this sense, what we can learn from this is that security cannot avoid being part of economics, in the sense that humans act, systems respond, and each of these events causes costs which drive further actions.

What it isn't saying is that we stop studying crypto and start studying economics; more like, study crypto, then use economics to apply that to the real world.