Rand Fishkin who ran Moz said on Twitter that back in the day, Matt Cutts (formerly of Google) "tried to get Mozcon not to invite black/gray hats to speak." It is an interesting point because I heard rumors like these with many conferences but yet, I've never seen a conference organizer say it publicly until now. I suspect maybe Google said if there are black hat speakers at the event, we won't send someone out.
I understand both sides.
Rand said it is important to get speakers to show their view of how critical they are about Google. Rand said "voices that criticize Googler's messages are important."
I suspect Google's view was that we shouldn't be teaching people how to take short cuts that might lead to their sites being penalized.
Again, I am not sure - these are just my guesses. I was not super involved in any conference planning when Matt Cutts was actively speaking at events. So I really do not have any inside information here - which is why I am writing about it.
But it does not surprise me that Google would have a rule - if you have black hat spammer related speakers offering tips on ways to trick Google, then they won't send speakers to that event. It does make a lot of sense. Google wouldn't want to be seen supporting an event like that in any way. At the same time, a conference can decide the speakers they want to bring in or not bring in.
Forum discussion at Twitter.