A rhetorical question is a question that doesn't expect an actual answer. It's said only to make a point, or to convey sarcasm, etc.
In English, a rhetorical question may be (inspired from the linked article):
A: we should vote for democrats this time
B: hah! what have democrats ever done for us?
Person B is clearly not expecting an actual answer. Their question is to be intended as "they never did anything for us". It is posed as a question to attain a rhetorical effect.
I'm honestly not sure about English, but in my native language a question in the form:
why would you do X
may be used rhetorically, and it would mean more or less "you shouldn't do X" or "please don't do X".
Does the same effect exist in Chinese with a 为什么 question? Can it be easily understood, given the proper context, or would it sound weird?
你为什么要浪费钱？(actually meaning "don't waste money")
I'm asking this because a native speaker pointed out to me that 为什么 questions primarily have a literal meaning and natives would hardly hear them as rhetorical. I realized I never actually paid attention to this.