>One operation can't corrupt another operation's view of state because state is immutable by default.
How true is this in practice? I mean on the one hand sure Operation 2 doesn't seem some half modified state from Operation 1. On the other hand Operation 2 now has some stale state and makes the wrong decisions does the wrong thing because it didn't see Operation 1's changes.
That happens whether immutable or not. In the mutable world, you have to guard that using a mutex or something. In that case, operation 1 may be blocked by operation 2, and now you get a "stale" state from operation 2. But that's okay. You'll get a new state next time. The real problem occurs when two states are mixed and corrupted.
How true is this in practice? I mean on the one hand sure Operation 2 doesn't seem some half modified state from Operation 1. On the other hand Operation 2 now has some stale state and makes the wrong decisions does the wrong thing because it didn't see Operation 1's changes.