Epic thread, maybe. But not in a good way; HBT is generally more helpful and a lot less insulting than this. While I would never brew with a setup like this, I couldn't criticize him either, since I don't know that it's actually bad.
I'm not a medical professional, or even know much about it, but I am skeptical about anything just assumed as common knowledge. So, a bit of googling turns up a few more facts:
- Iron, as posted earlier, is poisonous if too much is absorbed.
- Rust however is first insoluble and second not particularly harmful. Iron welders have a huge exposure to it from breathing in iron oxide fumes, and OSHA has concluded that's not very harmful.
- Cooking acidic foods in cast iron has been shown to leach in trace amounts of iron, usually considered a good thing unless you're one of the few people who already have too much.
All I can conclude is nation would be far worse off if he polished all the rust out of the kettle. But even in that case it's not clear there's anything to worry about; wort is only slightly acidic and nations large brew volume reduces the surface area.
Perhaps one of the more technical people here could run a few calculations on iron leaching rates based on a worst-case contact area, acidity, and boil time. I can't, but would be surprised if it turns out to be high enough for anyone to be worried about.
Again, I would never use a setup like this, and would happly suggest ways it could be improved or things he should worry about. But I wouldn't criticize unless I actually knew he's doing something dumb or bad.