That's too quick to be proof, of course, but I also think it's mostly too obvious to be worth spending more time on. The aspect that interests me is what Smith calls "grace." Grace is "the belief ... that Reality is ultimately on our side." I wonder whether something like this isn't inevitable. Of course it's possible to be unhappy, but there are limits. The truth of Silenus (that it is best never to have been born, and second best to die quickly) is a joke. It's a thought that is literally unbelievable except in the act of suicide. So life has to seem more good than bad.
Or is that right? Could you really wish you were dead but lack the will to die? Maybe, but I think it would be sort of crippling--would you take lots of drugs?, join the army and hope to be blown up?, just mope about all day? Lots of people wish their lives were better, but it's hard to imagine that many, if any, really want to be dead. Not that the limits of my imagination are much of an argument.
Aristotle has a kind of argument that life has to be believed to have a purpose or goal. In Book I chapter 2 of the Nicomachean Ethics he writes that:
If, then, there is some end of the things we do, which we desire for its own sake (everything else being desired for the sake of this), and if we do not choose everything for the sake of something else (for at that rate the process would go on to infinity, so that our desire would be empty and vain), clearly this must be the good and the chief good.Is he just assuming that our desire is not all empty and vain? Maybe he is, but this seems at least reasonable if not necessary for life.
So, however rough this sketch might be, it looks to me as though most people (perhaps everyone) is going to (perhaps necessarily) think that life is basically good and/or have some purpose to it, a goal that is not merely instrumental. Many people deny knowing what this goal is, of course, but then there's your mystery along with your grace. If only in Smith's sense, then, everyone not actively committing suicide is (or seems likely to be) religious. This means they think that the world is on their side, is fundamentally good.
And to think that the world is basically good is to think (isn't it?) that the world is basically good as it is. Which is a presumption against any argument that wholesale changes would be good. Which is something like a hint of an argument in favour of a kind of humble conservatism.
Or not an argument, I suppose. An argument against McMahan would more obviously lead to a belief of the form: if you do that things will be worse. My idea is more along the lines of: you literally cannot believe that. It would be an accusation of bad faith.
So, is this a (very) rough sketch of an idea with some promise, or what G. K. Chesterton called "a bewildering welter of fallacies"?