This is actually a good example why you should have a code of conduct as a conference. Bad things on stage happen. As an organizer, you can now write an apology that sounds like the one techcrunch wrote:

http://techcrunch.com/2013/09/08/an-apology-from-techcrunch/

Or, if you had a CoC, it could sound like this:

* "Sorry, we had people on stage that violated the rules we agreed upon beforehand. <list of rules from CoC> They were expelled from the conference immediately."