The original article wasn't talking about issues caused by storing too much program state in in-memory structures (variables/objects) though. It was talking abo

The original article wasn't talking about issues caused by storing too much program state in in-memory structures (variables/objects) though. It was talking about issues introduced by interactions with an external stateful system--a database. Bugs related to in-memory state that gets out of whack are definitely a hassle--especially in multithreaded situations--but are, in my experience, only the tip of the iceberg. Once you have that kind of issue under control (either by choice of platform, discipline, linting, or unit testing) there is a huge category of problems that can arise from the remaining surface, categorized loosely as "as soon as your code leaves its own memory space, it's part of a distributed system, with all the hassles that entails". Proclaiming that FP techniques resolve or even significantly ease that category of issue seems debatable at best, and a false promise at worst.