Either they are criminals (the worst of the worst, rapists, murders, pedophiles) or they are blameless hard-working heroes (say, doctors or professional basketball players from Australia in the N.B.A.).

The reality — and this should be obvious, but often gets overlooked — is that most migrants are in the messy middle with the rest of us. They’re good and bad, they’re parents and workers, and they’re mostly just trying to make life a little bit better for themselves and their loved ones.

This idea that they are somehow different and more extreme reflects little more than the political need for narrative and division. Beware of the packaging of simplicity.

“It’s a Fact-Free Zone”

When I was reporting a series of stories back in 2012 — the first to show that the era of mass Mexican migration was over — an expert I talked to warned that policymakers would ignore my findings.

Immigration, he said, is an issue driven by emotion. “It’s a fact-free zone,” he said. And he was right.

No matter how many cold hard facts get put into the public domain in the next few months — and I hope there are a lot of them — don’t expect the politicians to adjust their arguments. They’re appealing less to the head than the heart.

And look out for what’s missing too.

You probably won’t hear anyone, for example, pointing out that the decision to migrate is typically a long-term bet, calculated and paid for over several years, which rarely responds to immediate policy changes in predictable ways.