Functional programming with immutable state cannot possibly win in the general case.

There are two truths that ensure the dominance of imperative software:

1. At some level of software complexity, programmers MUST start to organize data into composite objects. They have to do this because working outside of well-defined problem domains is a recipe for buggy software and spaghetti code.

2. Copying memory around to enable to facilitate these immutable structures is SLOW.