This same argument is made against creating constructed languages. I've always thought David J. Peterson's Conlang Manifesto was an eloquent "defense" of the art, but this selection came back to me reading this thread:
QuoteI would hope that many would agree that doing something that neither harms the doer nor anyone else is not wrong. That said, creating languages, to my knowledge, has never resulted in the harming of another human being, or of the language creator .... Like any other hobby or activity, the only requirement is a requirement of time, and time management has nothing to do with the activity itself, but only with the one performing it. Thus, it can't be argued that language creation is "a waste of time", it can only be argued that certain people are wasters of time—how they do it is irrelevant.
So, the person "wasting their time" is the only one who can really judge whether their time is being wasted. If they are not harming anyone or being harmed (Where have I heard that?
), where's the harm in what they're doing, literally.