If someone introduces a counterexample that they believe is comparable, calling "whataboutism" doesn't refute anything. It's a move to exclude the information, and ultimately to stop discussion. What, after all, can one say in response? It isn't an argument—it's a label that is intended to stigmatize. This verbal trick is so empty that it's surprising it has currency among smart people. I think it's because the word itself is so catchy.

When someone brings up information isn't in fact comparable or relevant, the reasonable thing to do is to explain why it isn't, and give the other person a chance to respond. It's natural for people to disagree about what's relevant in an argument—that's part of having a disagreement in the first place. Trying to close off discussion so only your side's examples count as admissible isn't good discourse. Being first to raise a topic doesn't confer power to control the conversation.

Perhaps the more helpful broader point, though, is that all these canned arguments are repetitive and therefore low-quality. They're like slapping a sticker on something rather than engaging with it. Because of that, they make threads worse and more predictable. People tend to respond badly and strike back, rather than continuing in good faith—and it's easy to see why, because labels like "whataboutism" express dismissiveness.