Indeed, metaphilosophy [1] is the branch of philosophy which studies the questions of "what is philosophy?" and "why bother doing philosophy?". So far from being some kind of "forbidden question", this is a question which many philosophers have considered and sought to answer.
However, it seems like this is a discussion we're incapable of having here, which comes to the same thing.
If there's any branch of human inquiry where no question is off limits then it's surely philosophy. Debate about the practical application of philosophy has been part of it's fabric for it's entire history. The Greeks certainly regarded it as something that should inform one's life choices and I'm pretty sure that is one of the main areas of focus in Existentialism.