[jblow]

[q]In this case it means giving a voice to a racist advocate of slavery.[/q]

This is possibly disingenuous, and at least overly rhetorical.

They are not "giving him a voice" to talk about anything related to anything racist, and I'm sure if he used his slot to talk about anything racist, he would get perma-banned from the conference.

It is hard to say more than this without just repeating things said in the conference's statement. The idea is that a professional society ought to be able to cohere even when the members of that society disagree on matters outside the subject at hand. It seems like a good idea.