We should all stick to local food, this fellow was saying. Someone had asked what was on his mind, and it was dietary danger: tainted Chinese this and salmonella oozing out of that.

“Maybe we should be eating more like Grandma did,” he said.

He seemed bright: a computer analyst. You’d suspect he’d be up on a couple of realities.

One is that the state he and I live in, Wisconsin, has a winter. Gardens don’t grow here in the winter. Tough to eat a salad for about six months of the year unless you let California lettuce make big carbon footprints in our snow.

Also, if he was put off by what lax Chinese exporters were letting into the groceries, imagine what Grandma put up with.

More accurately, Great-Grandma, who, being pre-refrigeration, really did have to eat local. Or smoked, salted, or spoiled, and that, the experts say, is why stomach cancer was a leading killer a century ago and isn’t today.

Today, we refrigerate things and we have fresh fruit and vegetables year round.

Most of all, you’d think the guy would have noticed what’s on his license plate: America’s Dairyland. Wisconsin’s a great place to grow cows. It puts out far more dairy goods, particularly cheese, than its citizens can eat. Unlike giant Sunbelt dairies, its milk tends to come from mid-sized places that have some vague resemblance to your mental image of Old MacDonald.

Whether this is efficient and how much of this is because taxpayers are hit up for billions in farm subsidies is an argument for another day.

What’s plain is that we can react to risks in food in a rational way or an irrational one. We can hire some more inspectors, rethink standards, and address the problems.

Or we can all carry on about eating like Grandma, prattle about healing the Earth by eating only from one’s own garden, distrust anything grown farther than an ox-cart could have gone in a day, back in the day.

If the latter approach catches on — that appears to be a danger — there will be collateral damage. Most food is shipped from somewhere, for reasons David Ricardo explained: Everybody eats better if they specialize. The alternative is that the Catskills go under the plow while Iowa goes to waste.

If the whole notion of a world trade in food becomes suspect, setting off some eat-local trade war, this endangers a quiet, good new thing: American farmers earning a living by finding new customers overseas.

Christopher Gentine does this. He runs the Artisan Cheese Exchange. Based in Sheboygan, Wis., it links high-end American cheesemakers with buyers worldwide.

This isn’t big-volume business, says Mr. Gentine, but it’s growing. American makers do things that Europeans don’t — put jalapenos in brie, for instance.

Their reputation’s rising, as is demand in developing countries acquiring the means to eat well and selectively. Thus, Mr. Gentine makes sure the jalapenos didn’t come from the Sudan, and he talks terroir with visiting cheesemongers.

He is offering the world, he says, flavors distinct to specific places in America, sometimes distinct to a single dairy — but sold thousands of miles away. Globalization might be a bogeyman for a lot of people, but when it comes to exotic flavors, “they all want to be a little more globalized.”

On the other end of the size scale, there’s whey, the liquid that remains once the cheesy parts of milk turn to cheddar or gouda. Whey makes up nine-tenths of the milk by weight, and a few decades back, dairies would spread it on fields to get rid of it.

Now they sell it, for 70 cents a pound this summer. “The world has now taken more notice of whey,” Karen Endres of Alto Dairy, a huge Wisconsin farmer-owned cheese operation, says.

Dairies dry the stuff, concentrating the leftover protein. It’s an ingredient in a lot of foods. It gets shipped to China as high-quality pig feed. Ms. Endres estimates that every penny increase in the price of whey brings six cents more to farmers.

There are other new byproducts, too — whey provides lactose, as well, for making pills and baked goods — and the same could be said of other crops.

This parsimony of finding value in what once was waste is tied up with size and concentration. It makes sense for Alto to sell whey because it has so much and because it can find customers for it worldwide.

This serves even the ideals of people who would reflexively dislike any food described as a byproduct. It helps smaller farmers stay in business, it lets dairying take place where the climate and water supply are suited for it, and it provides protein to a hungry world out of what would have been waste.

And as with exporting unique smoky bleu cheeses from Oregon, as Mr. Gentine does, it trades on quality.

If it is fear about riskily bad food that moves us to abjure food from afar, we need to remember that it is trade that makes available to us things better than what we can get locally.

The flatter the dairy world, the more American producers’ known high standards count. Free trade lets customers buy better.

Forswearing trade means you’re stuck with what you’ve got nearby — good, bad or, in a Midwestern winter, a lot of root crops.

Mr. McIlheran is a columnist for the Milwaukee Journal Sentinel.