The allegations are published and the OP links to the original complaint on Medium: https://medium.com/@nodebotanist/why-i-won-t-be-speaking-at-...
Furthermore, the best defense against libel is the truth. Part of the complaint is an opinion based on public statements made by Crockford (the "slut-shaming"). The other published complaint is that Crockford said to the complainant before her talk, "the talks as the day went on just got stupider and stupider.” Unless he can convincingly prove that he never made such a statement to the complainant, he's not going to have much of a libel case. He could argue damages based on "false light", I suppose. [0]
On a (computer-related) technical standpoint, I disagree with what you think is the right reason ban a technical speaker, e.g. Crockford "for his stated prejudice against comments in data-interchange formats". That's the kind of strong diverse opinions that a tech conference should be thirsty for, just like a Ruby conference should be thrilled to have Edsgar Dijkstra talk about object-oriented programming.
But if someone says, "People who think comments belong in data interchange formats are fucking morons"...Yeah, I could see why some conferences wouldn't invite them.