Someone needs to inform this author that commodity options trading is totally a real thing that actually happens, not a hypothetical. It doesn't happen in precisely the way he supposes, but the some of the absurdity of his supposed food contracts evaporates when you realise that people actually do speculate on the future price of chicken, yet the world food market has not crumbled.
While you can technically trade commodity futures, they're not really analagous to a mortgage in many ways.
1) They're not useful for retail consumers. One futures contract on wheat is 5000 bushels. You could use them for pure speculation, but unless you own a 5000 acre farm or are General Mills, they're not helpful from a cost-hedging perspective.
2) They mostly trade short dated, 1 year and less. This makes them more analagous to a one or two year lease than a 30yr mortgage (though some futures contracts trade as long as 7 years).
3) Futures are marked to market, and you have to post daily margin. Your bank won't ask you to pony up 50k if the the price of your 500k home falls 10%.
I don't think long dated mortgages are evil, but I can appreciate that they can be market distorting.