Another week, another battle in the pundit wars.

In the hothouse of polarized partisan combat that is American public life in the Trump era, nothing inspires outrage like a mainstream media outlet publishing a column or hiring a columnist who regularly takes positions contrary to those favored by … progressive journalists.

Bret Stephens regularly inspires this fury, starting nearly a year ago with his very first column for The New York Times, in which he expressed a modicum of skepticism about the proper policy response to the science of climate change. Stephens' colleague at the Times, Bari Weiss, regularly provokes similar convulsions of outrage, and never more than for a tweet during the Olympics in which she referred to figure skater Mirai Nagasu, a Japanese-American who was born in the United States, as an immigrant.

And now it's Kevin Williamson's turn to endure his portion of progressive hate — in his case due to a now-deleted tweet from 2014 in which he suggested that women who have abortions should face capital punishment, preferably by hanging. Had Williamson not been recently hired away from the proudly right-wing National Review by The Atlantic, this shockingly extreme tweet would have remained where it had ended up — down a memory hole, barely recalled even by those (like me) who criticized it at the time. But because Williamson's byline will soon be appearing in a prominent mainstream media outlet, the tweet has resurfaced, and the response has been blistering.

Some of this response has been crude and thoughtless — a caricature of left-wing illiberalism that resembles nothing so much as the 19th-century Catholic Church's view that "error has no rights" (with error of course defined by the person making the claim). Much better have been those that attempt to delineate precisely which lines Williamson crossed with his deleted tweet — and what the consequences will be of The Atlantic giving him a much more prominent platform.

Michelle Goldberg, for example, penned a thoughtful column that reflected on the way the elevation of people who hold marginal views can end up putting what should be untouchable first principles into question among a large audience of readers. Along the way, Goldberg quotes feminist writer Jessica Valenti making the similar point that there's a grave danger in treating "our lives and freedom" as just "abstract concepts" or something "to be debated" rather than as "given."

The sentiment is eminently understandable. No member of a vulnerable population wants to think that civil protections against violence enacted by other individuals and groups, or by the government itself, should be up for discussion, let alone that they could be rescinded by political fiat.

Yet there is also something naïve and self-deceptive about this way of thinking about politics — a naïveté and self-deception that's lamentably widespread among progressives.

This way of thinking about politics informs Valenti's hope and expectation that her reproductive rights will be treated as a "given." It's also at work in Barack Obama's famous (and often repeated) line about how history "bends toward justice" — with justice defined in terms of an ever-lengthening list of groups demanding and receiving political rights and social recognition. The presumption of this view is that once such rights and recognition are granted (as a result of changes in public opinion, favorable court rulings, or both), they become irreversible, settled, a new baseline in the ongoing struggle to bend the arc of history ever-further in the direction of justice.

Far from being limited to first principles, this outlook extends even to policy debates. Recall Al Gore proclaiming confidently more than a decade ago that the debate surrounding climate change is over, with the science and proper policy responses firmly settled. It was this conviction that Bret Stephens dared to question in his Times column about climate science that sparked an uproar.

Whether the issue concerns public policy or the fundamental moral principles undergirding American public life, progressives tend to presume that their own positions deserve to be treated as lying beyond the give-and-take of political disagreement and debate.

What the rise of a less liberal, more radical, intransigent, and populist right is forcing progressives to confront is that this way of conceiving of democratic politics is a fiction. Nothing in democratic politics is given — or rather, the things we consider given at any moment enjoy this status for no more exalted reason than that public opinion (expressed primarily through elections) favors treating it as such. But the settlement or consensus in its favor is always temporary and contingent. The contestation of politics, the struggle over power and ideas, over the Constitution and the law and who we are as a political community, never ends. It's always possible for a settlement or consensus at one moment of history to be rethought, overturned, or reversed. Rights granted can later be rescinded — and there's no way to prevent that from happening beyond continuing the fight, day after day.

History isn't an arc slowly bending toward justice. It's a battlefield on which a skirmish line shifts back and forth in an unending contest between ideological combatants. The agonistic character of politics becomes concealed during eras defined by consensus, when the skirmish line stays in much the same place, shifting only slightly or fairly slowly from year to year and decade to decade. But such eras are the exception in history — or at least never more than a temporary interlude between periods of more rapid or intense struggle.

Since Donald Trump's election to the presidency, we've entered a period of renewed political combat after several decades of comparative placidity — a time when the string of victories enjoyed by progressives on social issues since the middle decades of the last century faces potent, organized opposition. In such a situation, the best response to an outrageous right-wing argument is not to insist that the person defending it should be denied an opportunity to make his case, or to lament that more people don't treat the progressive position as a given, or to follow the lead of Barack Obama in issuing watery proclamations about how "that's not who we are." The best response is to mount the most rhetorically and logically formidable counterargument against the right-wing provocation.

Some on the left will undoubtedly say that this leaves progressives in a politically vulnerable position. That's true — but the alternative in politics isn't between political vulnerability and invincibility. It's between those who deny the vulnerability — the contingency and provisional character of all political "victories" — and those who accept it, and wage the battle accordingly, with their eyes fully open.