It seems like both the original e-mail and the response were both within reason actually. Remember the second e-mail was not just responding to the first e-mail, but also to the reaction to the first e-mail.
Email 1 tldr: You might not realize that people find your cultural stereotypes offensive, please be considerate (although the explicit list of costumes felt a little too much like trying to give a pre-approved list of costumes).
Email 2: Not all things that are offensive should be banned, engage with people.
I however suspect that on the student level the discourse seemed much less civilized which is why the whole thing is blowing up.
I actually don't think the blond-haired girl example is a complete straw man. She was just trying to show that there was a large area between "probably okay" and "probably not okay" where people probably weren't able to agree, but people could still put outer bounds on. Also while this might not have been a complaint in the original e-mail, it very well could have been a complained the reaction to the first e-mail generated.