You can't build products without mutable state. How far should we go when we reason about global mutable state? Do we go as far as the database layer? Computers

You can't build products without mutable state. How far should we go when we reason about global mutable state? Do we go as far as the database layer? Computers are state machines and I don't know why we're so eager to get away from that. Separation of concerns and interfaces/protocols help, but somewhere down the line, it's accessible, mutable, and it's stateful.