Imperative > pure functional programming

Who would intentionally write code where you can't randomly access memory?  People who prefer O(n log n) over O(n) algorithms.

I like functional programming because it allows me to guarantee the functioning of pure functions for as long as I understand the underlying logic. I can then spend the rest of my time figuring out mistakes in the impure functions or learning about how to optimize the software from naive implementations to more efficient ones.