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 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.

[Farhad Manjoo answered your questions about this column on Twitter.]

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 President Trump’s racist immigration rhetoric not just by fighting his wall and calling for the abolishment of I.C.E. but also by making a proactive and affirmative case for the vast expansion of immigration.