Like you said, functional programming isn't hard, but I think the problem is that learning a completely new language with an unfamiliar syntax and abstractions

Like you said, functional programming isn't hard, but I think the problem is that learning a completely new language with an unfamiliar syntax and abstractions is hard, and trying to apply functional programming techniques in most current mainstream languages is equally hard. The fundamental language feature that makes true functional programming possible is first class functions, since that allows higher order functions and anonymous functions. The lack of that feature in most mainstream languages is why functional programming feels so foreign to most programmers. Sure, you can write functions without side effects, but making good use of them without polluting your namespace, explicitly passing around function pointers, or having lots of extra boilerplate code lying around is difficult in a lot of languages. That's constantly changing though. I think as more languages start adding support for higher order functions, even established languages like C++ and Java, we'll see more and more people using a functional style and less nonsense discussion about how "hard" it is, because it really isn't hard at all. Already, you see bits and pieces of functional Javascript code littered all over the Internet on a regular basis. In fact, I'm willing to bet that at some point in the future, functional programming techniques be considered easier and more natural than a purely imperative approach, simply because more programmers will have encountered it sooner in their programming careers and made effective use of it. It'll be an everyday occurrence to meet a programmer who uses anonymous functions for callbacks and commonly makes use of fold, reduce, and map instead of explicit loops and state variables. Meanwhile, meeting someone who knows what a pointer is or even how to manage heap memory will be a one in twenty event, and chances are that person will be an embedded developer who also knows how to write interrupt handlers and even a custom, deterministic memory allocator for real time applications.