Well, if the functional code people are complaining is on the same level as the one the author used on the post, then I agree that a quick pair session is enoug

Well, if the functional code people are complaining is on the same level as the one the author used on the post, then I agree that a quick pair session is enough to "solve the conflict". But IMO there is problem when (assuming Scala here) you include a library like Scalaz on the codebase, and then start using more abstract functional concepts. While I think these concepts are amazing, I usually don't use then on my day job as I know that my team don't have the knowledge nor the timing to quickly grasp such concepts without impacting the project's pace.