There's no convincing him, there's only an opportunity to make him look absurd publicly. Because he doesn't really believe the stuff he's saying, he takes pride in derailing conversations with points they prey on fears of losing money. My whole goal in responding to him is no make him look bad while staying on topic. Things like...  veiled jabs about him getting sued, taking a piece of what he said out of context to make my point, finding agreement with him on a point he wasn't making, and other similar derailment responses are among my favorites.