The argument isn’t that state is bad or doesn’t need to be managed. It’s more that spreading that state over a large number of areas leads to a lot of complexity and cognitive overhead in terms of expected behaviour at any given point of execution. Functional programming gives you ways to be much more explicit about the transformation being performed and the before/after states (except arguably when you start getting overly cute with zippers and lenses and such). To the extent that this approach hasn’t magically transformed programmer productivity or software quality, we know that both approaches are admissible.