Kent Kent the Elephent

Even if it's rhetorical?

Yes. The reason why English speakers often don't put question marks is not because it may be rhetorical but because in English the voice goes down and not up at the end of many questions, making the question sound more like an indicative sentence. Quite often, this is for casual and routine question, like certain uses of 'how are you' or other set phrases like 'what would I do without you?' and can indicate a lack of curiosity, e.g. when it's polite to ask how someone is but the speaker also wants to show that they're not probing.