Your reaction was perfect. Stay friendly, but stop the discussion. Sentences like "Ok, we have different opinions and can't sort that out right now" or something on that line work perfectly well. Make clear, you want to stop the discussion. Maybe claim that you don't have enough information and will "read something about it".
Ideas like "he has it in his blood" can't be changed within a short discussion anyway. You would have to run against a wall, which is protecting the persons wrong views since her childhood. To change them would make it necessary to rethink everything and give up too much.
I'm not that nice though. I look up people slowly from head to feet and my faces makes very clear what I think. But that way people feel offended easily, so not to be recommended.
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Deep into that darkness peering, long I stood there wondering, fearing,
Doubting, dreaming dreams no mortal ever dared to dream before (E.A.Poe)