[Raak] You're dismissing Belle Waring's arguments because she uses "libertarian utopia" as a tongue-in-cheek description of the kind of society that Epstein, Barnett and Friedman are discussing. But leave that phrase aside if you like: I think her one paragraph synopses of their arguments is pretty close to the money.
As an economist, I am sympathetic to the view that we should encourage the value-creating possibilities of private contracting between individuals, and as a social liberal, I am sympathetic to the view that we should limit government intrusion into private decisions. Those are positions that loosely ally with libertarianism. But I am also aware that, in the real world, private transactions frequently have significant consequences beyond the transactors, and libertarian arguments start crumbling rapidly one you take this seriously. (Epstein recognizes this in his contribution, and so ends up advocating a form of state that is not really that different from what we already have; he would simply like to see less government regulation.) The key paragraph from Belle Waring's argument is surely this, though:
Now, everyone close your eyes and try to imagine a private, profit-making rights-enforcement organization which does not resemble the mafia, a street gang, those pesky fire-fighters/arsonists/looters who used to provide such "services" in old New York and Tokyo, medieval tax-farmers, or a Lendu militia. (In general, if thoughts of the Eastern Congo intrude, I suggest waving them away with the invisible hand and repeating "that's anarcho-capitalism" several times.) Nothing's happening but a buzzing noise, right?
I am completely with her here: it is at this point that I think libertarianism utterly loses touch with reality. Private contracting without some institution to enforce contracts is infeasible, and private provision of contract enforcement strikes me as much scarier than enforcement by a democratically elected government. (Perhaps that's what comes of visiting countries where ordinary restaurants are guarded by men with sub-machine guns.)
Oh, and you are completely misreading Brad DeLong. He is not saying that Smith, Hume, Hobbes, et al. couldn't imagine a world without government; he is saying the exact opposite. He is saying that they know it to be a crazy idea because they can imagine it all too well.