This is nonsense. What does entitle someone to be called "a writer" other than, you know, writing things? If you're writing - you're a writer. If you've practiced enough to develop good skill - you're a good writer. If you've found a way to make money with it - you're a professional writer.

Writing is never bad for you. It's like saying that you shouldn't be pretending to be a programmer, when you know you arent. What the fuck does that even mean?

First you aren't a writer/programmer. Then you pretend to be a writer/programmer, by attempting to do what writers/programmers do. Then, if you keep doing it long enough, you become one.