So one of the problems is indeed that insurers have conflicting incentives, as you correctly described one of them, and it's possible (although I don't know enough to argue either way) that ACA actually made this worse. I think one of the big arguments for a single-payer system, or at least the "public option," is that those middlemen could (ideally, in theory) embrace the position they're in to fight for lower costs without the conflicting incentives that come with being a for-profit entity. I guess that's basically what Noah Smith (author of the parent's linked article) is saying in his conclusion. There are, of course, other arguments for and against. Healthcare is a fascinatingly (and maddeningly) complex problem.