Saying "you're wrong" isn't the issue here. Saying "your mom should have aborted you and i hope you die" is the issue. I don't think people in cultures where losing face is a big issue much care if they're told they're wrong. They care is they're told they are so wrong they should kill themselves or be killed. Honor killings are unfortunately still a big deal in some parts of the world.
What you say in defense of the mailing list insults is the same thing that has been said about casual racism or casual misogyny in other groups normally dominated by white men. It scares away other groups and cultures, and it's not acceptable anywhere.