Core to their argument is that most things we care about in society have increasing returns to scale so that under our current system we systematically under-allocate and mis-allocate to public goods.
While I disagree with a lot of it in practice, I highly recommend reading it if you're thinking the way the parent comment of this comment does.
Posner is probably best known for (a) suggesting an open market for babies, and (b) being one of the smartest humans of our era.
He's a Chicago School market-mechanisms fetishist, but a reasonable one believing in the necessity of regulations to tackle externalities and anti-trust.
His writings sit in that perfect spot where I instantly notice the author is way smarter than me, but can still understand the jokes.