Should we consider the decline of "aggregate violence" as proof of the fact that modern states, on balance, "saved" more people (by pacifying nations) than killed them (by, well, killing foreign civilians, Jews, Gypsies, class enemies, and kulaks, among others)? One point and one question. First: there is no question that the modern state is a highly successful institution. It has solved some problems, this is why it still survives and, though a rather recent artifact, it appears as immutable and eternal in the eyes of most. Second: how much of the decline in "private" violence (that is: coercion by unorganised individuals over unorganised individuals) can be directly traced to the institution of governments? And, even so, should we really infer that the more you spend and regulate, the more violence declines?
Back to Ridley's work. "The Evolution of Everything" is a rather different book than "The Rational Optimist". "The Rational Optimist" dealt by and large with facts; "The Evolution of Everything" deals with ideas. I found it a very enjoyable, and challenging, book. Ridley conceived it as a book to counter "skyhooks," defined as "devices for explaining the world as the outcome of design and planning."
Central planning and over-regulation are among Ridley's "skyhooks."
This might recall a comment Herbert Spencer made in Social Statics: "...idolatry is a mode of thought under which all causation is attributed to entities." The idea that all causation is attributed to entities is a powerful ally of interventionism, as it attributes to government the power of shaping and molding society and the economy.
This is why Spencer thought that the "development of politico-economical science" should be applauded as a victory of "natural philosophy over superstition." The same is true for Ridley's book.