Rhetorical questions are "Questions that do not require an answer, but are only put in the form of a question in order to produce a greater effect" (Bradley's Aids to Latin Prose, cited OED). Rhetorical, indeed, is the adjective from rhetoric, the art of making speeches, and speeches are where you may expect to find rhetorical questions most often, if not always wisely. A politician who says, in a speech, "Are we to approve of this monstrous proposal?" is not expecting to hear a response. It is to be expected that the mood of the audience will follow the implication of the speech - that this 'monstrous' idea cannot possibly meet with approval.
There is always the danger in the speech that the audience - or one heckler in it - will react in a way contrary to the speaker's intention. Whether to ask the question is to an extent a matter of the speaker's judgement of the mood in the audience. If the audience is hostile, the speaker is wise not to ask the rhetorical question, but to form it as a statement.
What is true of a speech is even truer of the written word. You are advised not to use rhetorical questions in academic writing. They are a weak form of argument; and you cannot assume that all readers of your work will agree with you. Consider the response if a reader thinks the 'wrong' answer to the question. Indeed, questions in written English are usually a mistake.
Some rhetoricians have given the labels erotesis (or erotema) and anacoenesis to rhetorical questions. These appear to AWE to be unnecessary to ordinary users of English, although they do have subtle refinements of meaning. The former, erotesis, "is a figure of speech by which a speaker, in the form of an interrogation, boldly asserts the opposite of what is asked; as "Creditis avectos hostes?" (OED - the Latin means 'Do you think that the enemy has been carried away?'). In other words, an erotesis is a 'rhetorical question that expects the answer NO'. Anacoenosis is "A figure in rhetoric, by which the speaker applies to his hearers or opponents for their opinion upon the point in debate" OED.