Here is in summary his "crime" a letter his wife wrote:
https://www.washingtonpost.com/opinions/my-halloween-email-l...
https://www.thefire.org/email-from-erika-christakis-dressing...
"Nicholas says, if you don’t like a costume someone is wearing, look away, or tell them you are offended. Talk to each other. Free speech and the ability to tolerate offence are the hallmarks of a free and open society."
They are both right. People who opposed them are wrong. They should be ashamed of themselves.