That was exactly the point I was trying to make. "What about" arguments can be valid.
Splitting hairs, he was specifically referring to the deflection-style "what about" argument, as if the sins of others justifies one's own.
How does one differentiate "deflection-style 'what about' arguments" from valid "what about" arguments free from bias?
If that was a serious question and not a troll, check philosophy courses; should be some online. They have a bit of history in that discipline of logic and analyzing arguments...
I wasn't trolling. I was just pointing out that it seems like a subjective distinction as a practical matter and asking if there was a way to make it less subjective in the context of online comments, argument rebuttals, etc.