Snapedom

And it's perfectly ok to challenge that. Go for the content, but don't get personal. Mary didn't say: posterxyz is a coloured woman. I don't know why she identifies... She said: coloured women identify...
So, if you reply: you are wrong: coloured women don't identify and white women are privileged... that would be ok. But waxing on your journal, on wank sites, whereever about what 'mary_j said' will only upset people but not make them want to listen to you.
The unpersonal approach is a lot less offensive and doesn't heat up discussions as the personal approach does. That way, people are usually more open to listen and learn. If that is what you want.