I don't claim to be very experienced in functional programming, but doesn't his whole argument simplify to "State is hard in a pure functional setting" ? I was

I don't claim to be very experienced in functional programming, but doesn't his whole argument simplify to "State is hard in a pure functional setting" ? I was under the impression that this was a simple and fairly well understood problem. Either use a functional abstraction for state, a reduce with state or perhaps a monad if the state needs to be carried through many types of operations, or manage it in an impure way, using STM with a global state perhaps. I don't see how this is any knock against the functional programming paradigm. I always understood the rule of thumb to be "use purity as much as possible, and be impure only when it's explicitly needed." Modifying a global state seems to be a pretty obvious case for using an impure function. Am I misunderstanding this?