This style of argument is deflection, and it gets us nowhere.
It's very effective in redirecting the focus away from one bad actor and onto another bad actor, though.
In reality, comparables sometimes are and sometimes aren't relevant. You have to make that argument case by case for it to have any meaning. Invoking a generic word as if it magically decides the matter is just the sort of thing the HN guidelines ask commenters not to do.
To pick an example from another, hopefully distant enough, flamewar topic: if someone complains that dynamic programming languages have runtime errors and someone replies, "what about null pointer exceptions in $static-lang?", it's reasonable to argue about whether and how that is comparable. What's not reasonable is to exclaim "Whataboutism! The topic is errors in dynamic languages. Stop trying to change the subject." That amounts to "you can't say that because I spoke first", and that's not how conversation works. The question of what's relevant is an intimate part of the discussion itself. It's not something that whoever-spoke-first gets to control. Indeed, if anyone did control that, they would have the power to control the entire conversation. Past explanations for anybody who wants more:
https://news.ycombinator.com/item?id=19862258
https://news.ycombinator.com/item?id=19471386