>It's theoretically possible that the 'f()' or 'x' might change between the lazy evaluation of step one and the lazy evaluation of step three million.

You can't re-bind values in the lambda calculus, so no, they never will change. This is why languages like haskell are immutable.

His complaint #3 also relies on the false assumption of a mutable language.

Complaint #4 was solved by monads, quite a while ago.