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.
Like GP said, it derails discussions into talking about a different bad actor than the actual one committing the bad behavior, while (intentional or not) minimizing said behavior. In short, just because the bad behavior exists elsewhere does not justify doing the bad behavior, or makes it any less bad, and the act of pointing it out can be a poor attempt at distraction from culpability.