Whataboutism isn’t a fallacy and is widely misused online.
If someone says “I think x should stop because of y”. It is a valid argumentative response to say “y also occurs with z, so should z also stop?”. It is argumentatively revealing either hypocrisy, or that the original imperative relies on additional, unstated arguments/assumptions/biases.
I don’t think that’s whataboutism?
Maybe I’m confused, but I thought whataboutism was more like “you are saying I am doing X bad thing? What about Y bad thing you’re doing, let’s discuss that instead”.
It’s a deflection technique, not a check on logical consistency.