“How is NAFTA good for your children and grandchildren?” A very direct – and insightful – question asked by U.S. Trade Representative Robert Lighthizer at a recent round of NAFTA talks, according to an account in last week’s Wall Street Journal.

Patrick J. Ottensmeyer, a railroad executive who described the incident, offered his own response in an op-ed. He cited the usual statistics: U.S. farm exports to Canada and Mexico have quadrupled since NAFTA lowered tariffs in the 1990s. Without this trade agreement, he wrote, the billions of dollars in goods and services that we now sell to Canadians and Mexicans “would be replaced by products from other markets,” such as Europe and South America.

All that’s true. I’ll even take it a step further: Without NAFTA, America’s agriculture-dependent heartland would sink into a new depression.

We’re already struggling. Although our yields are booming—right now, I’m harvesting what may be my best corn crop—commodity prices are low. They’ll sink even lower if supplies stay high and demand shrinks.

So here’s what I’d like to say to Mr. Lighthizer if he were to ask me the same question about the benefits of NAFTA, as a farmer and consumer, for my children and grandchildren.

My father started our farm in 1932 and I’ve worked on it my whole life. That makes us relative newcomers here in northeast Iowa: Lots of my neighbors inhabit sixth and seventh-generation farms.

We share a lot of concerns in common. Which seeds should we plant in the spring? Will the summer be wet or dry? How will our equipment hold up as we drive it through our fields?

Here’s one question we all worry about: Can we pass on our farms to our kids and grandkids?

I’m now trying to turn my second-generation farm into a third-generation farm, as I train my 31-year-old son in the business of agriculture.

Growing up, he didn’t show much interest in farming. He even went to California and started a career in the computer business.

Then I told him that if he ever had thought about coming home and taking over the family business, now was the time: He had a lot to learn, and I still had few more good years to teach him. He would have to drive the machines, lay down the fertilizer, and meet with the seed, fertilizer, machinery and so on salesmen. I figured that it would take five to ten years for him to pick up what he needs to know.

It turns out that he’s pretty good with technology. As agriculture advances with its self-driving tractors and satellite mapping, I can barely keep up. Yet he’s at home in this world of rapid change.

One thing never changes, though: the laws of economics. If we pull out of NAFTA, new tariffs will cut us off from some of our best and most reliable customers. Farmers everywhere will hurt—and it will devastate the youngest farmers, like my son, as they try to begin a life in a sector that’s competitive even during the best of times.

I also wonder about the future of NAFTA for my daughter and granddaughter. They won’t become farmers, but they’re consumers. Their whole lives, they’ve enjoyed abundant food and choices. They don’t know a world in which they can’t buy just about any kind of fresh produce at just about any time of year. Grapes in the winter? No problem. Americans can find them at their local grocery stores, thanks to international trade.

As we approach Thanksgiving, I’m thankful for NAFTA. I’m also hopeful that we can modernize the agreement. I’m perfectly willing to let Mr. Lighthizer try to make it even better.

Yet I’m troubled by the idea that we’re taking NAFTA’s blessings for granted. If we pull out of this successful trade agreement, our choices as consumers will diminish. Our rural economies will collapse. And our family farms—including mine—will suffer.

Right now, folks are scared. And if you’re not, you should be. One week, we hear that talks are proceeding well. The next week, we hear that they’re falling apart. We don’t know what to believe—and the occasional threats of withdrawal keep us awake at night.

So is NAFTA good for my children and grandchildren? You bet it is.

We don’t want NAFTA. We need NAFTA.