Can a 为什么 question be rhetorical in Chinese? 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 &quot;they never did anything for us&quot;. 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 &quot;you shouldn't do X&quot; or &quot;please don't do X&quot;.
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 &quot;don't waste money&quot;)

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.
你为什么要浪费钱？standalone doesn't look it, whilst 你为什么浪费钱？does.
你为什么浪费钱？can be a blame or scolding, implying that there is no reason for you to waste money hence it's a rhetoric.
Also, Tone and context play important roles.  Your original sentence might be a rhetorical question if the proper tone is applied in a proper context.
However, the native speaker you asked has some point there.  为什么 is kind of on the borderline.  You can interpret both ways sometimes.
It's worth to mention that 为什么不xxx  is a common rhetorical device.  E. g.

A: 你要吃吗？
B: 为什么不呢？


A: 你会去吗？
B: 为什么不去呢？