I recently saw a post that made me think the same thing. I think it was about a transformerless power supply.
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Just to be clear, the OP of the circuit of the thread I spoke of did post warnings, quite a few in fact. I suspect that despite the warnings, some people will choose to ignore them for what ever reason, be that English is not primary language or maybe the circuits get copied to Google images and the warnings are not transferred.
Be that as it may, I think adding warnings is a good idea, but how would you enforce such a thing, the mods have enough to do as it is, and this may be just another burden of their time?