At my support group we had one of those come a few times. No one ever responded to what he said, just redirected to a different topic. He was reminded that people were not to monopolize the time in group. He gave up after a few weeks and stopped coming. We also had one guy come in saying he had the cure for bipolar - Concerta. People did respond to him and explained what Concerta was and that it wasn't a cure. He also only came a few times. The people with agendas usually don't come very often.