I agree with Pamela that what's appropriate in a business setting is not always going to work with a social group, which is really what most guilds are. I don't like the idea of intentionally embarrassing anyone, but the person "in charge" should step in and stop the chit-chat if it is interfering with the speaker or with the business meeting. Just banging the gavel and saying "there are too many side conversations going on for some of us to hear the speaker" should do it.