Rhetorical questions are generally difficult to deploy effectively in a piece of writing. When debating with someone over the Internet their use is particularly ill-advised, for at least three reasons.
Reason #1: Would clarity benefit from rephrasing as a statement?. Clarity benefits if you rephrase as a statement.
You can probably rephrase what you mean as a statement, which will be clearer and more explicit. Go on, try it. Rephrase your rhetorical question, and add your answer. The person you are arguing with now has less chance of missing what you are really trying to say. Communication is hard. Communicating with someone who disagrees with you is extra-hard.
Clarity benefits if you rephrase rhetorical questions as statements.
Reason #2: Isn’t it obvious what I mean?. It isn’t obvious what you mean.
In our face-to-face communication we rely on a bunch of non-verbal channels to convey additional information. This is crucial when what we mean is different from exactly what we say. In written language these channels – tone of voice, gesture, etc – are missing. Moreover you can be less certain of what your audience knows or assumes. For these reasons, things like sarcasm are notoriously difficult to pick up on over the Internet. Like sarcasm, rhetorical questions assume a shared understanding to allow you to convey what you mean without stating it explicitly. So, by using a rhetorical question you are taking a risk that your real meaning will be understood by your reader. That is an unnecessary risk, don’t take it.
It isn’t obvious what you mean. Rhetorical questions ask your reader to infer your real meaning. Be kind, just tell them.
Reason #3: Don’t we all know the answer to this one?. We don’t all share the same assumptions.
Rhetorical question assume a shared framework, something you cannot assume when you are disagreeing with someone. If you want to focus on the substantive disagreement you have with someone, don’t dance around it with rhetorical questions. Say what you mean so your reader can respond based on that, rather on what they have to guess about the inspiration for your questions.
The clue is in the name – rhetorical questions are for rhetoric, persuading an audience, a passive mass rather than a particular individual who has the right of reply. If you are arguing on the Internet you should have the courtesy not to treat a singular reader or small group of readers who want a right of reply as an audience. They have a considered opinion which you need to listen to. They may even want to understand what your considered opinion is. You do them – and your opinion – a disservice if you deploy rhetorical questions, which obscure your meaning in favour of self-satisfied point-scoring.
No, we don’t all the know the answer to your rhetorical question. We don’t agree, so we probably don’t share common assumptions. Rhetorical questions assume we do, so you should particularly avoid them in argument.