The internet expands the bounds of acceptable discourse, so ideas considered out of bounds not long ago now rocket toward widespread acceptability. See: cannabis legalization, government-run health care, white nationalism and, of course, the flat-earthers.

Yet there’s one political shore that remains stubbornly beyond the horizon. It’s an idea almost nobody in mainstream politics will address, other than to hurl the label as a bloody cudgel.

I’m talking about opening up America’s borders to everyone who wants to move here.

Imagine not just opposing President Donald Trump’s wall but also opposing the nation’s cruel and expensive immigration and border-security apparatus in its entirety. Imagine radically shifting our stance toward outsiders from one of suspicion to one of warm embrace. Imagine that if you passed a minimal background check, you’d be free to live, work, pay taxes and die in the United States. Imagine moving from Nigeria to Nebraska as freely as one might move from Massachusetts to Maine.

There’s a witheringly obvious moral, economic, strategic and cultural case for open borders, and we have a political opportunity to push it. As Democrats jockey for the presidency, there’s room for a brave politician to oppose Trump’s racist immigration rhetoric not just by fighting his wall and calling for the abolishment of ICE but also by making a proactive and affirmative case for the vast expansion of immigration.

It would be a change from the stale politics of the modern era, in which both parties agreed on the supposed wisdom of “border security” and assumed that immigrants were to be feared.

As an immigrant, this idea confounds me. My family came to the United States from our native South Africa in the late 1980s. After jumping through lots of expensive and confusing legal hoops, we became citizens in 2000. Obviously, it was a blessing: In rescuing me from a society in which people of my color were systematically oppressed, America has given me a chance at liberty.

But why had I deserved that chance, while so many others back home — because their parents lacked certain skills, money or luck — were denied it?

When you see the immigration system up close, you’re confronted with its bottomless unfairness. The system assumes that people born outside our borders are less deserving of basic rights than those inside. My native-born American friends did not seem to me to warrant any more dignity than my South African ones; according to this nation’s founding documents, we were all created equal. Yet by mere accident of geography, some were given freedom, and others were denied it.

“When you start to think about it, a system of closed borders begins to feel very much like a system of feudal privilege,” said Reece Jones, a professor of geography at the University of Hawaii who argues that Democrats should take up the mantle of open borders. “It’s the same idea that there’s some sort of hereditary rights to privilege based on where you were born.”

I admit the politics here are perilous. Although America’s borders were open for much of its history — if your ancestors came here voluntarily, there’s a good chance it was thanks to open borders — restrictions on immigration are now baked so deeply into our political culture that any talk of loosening them sparks anger.

People worry that immigrants will bring crime, even though stats show immigrants are no more dangerous than natives. People worry they’ll take jobs away from native workers, even though most studies suggests that immigration is a profound benefit to the economy, and there’s little evidence it hurts native workers. And if we worry that they’ll hoover up welfare benefits, we can impose residency requirements for them.

But these are all defensive arguments, and when you’re on defense, you’re losing. For opponents of the president’s xenophobic policies, a better plan is to make the affirmative case for a lot more immigrants.

Economically and strategically, open borders isn’t just a good plan — it’s the only chance we’ve got. America is an aging nation with a stagnant population. We have ample land to house lots more people, but we are increasingly short of workers. And on the global stage, we face two colossi — India and China — which, with their billions, are projected to outstrip American economic hegemony within two decades.

How will we ever compete with such giants? The same way we always have: by inviting the world’s most enthusiastic and creative people — including the people willing to walk here, to risk disease and degradation and death to land here — to live out their best life under liberty.

A new migrant caravan is forming in Honduras, and the president is itching for the resulting political fight.

Here’s hoping Democrats respond with creativity and verve. Not just “No wall.” Not just “Abolish ICE.”

Instead: “Let them in.”