I don’t tolerate the phrase “America is a melting pot” in my students’ essays. It’s a historically questionable and largely meaningless cliché. But at a number of schools—including the University of California, Purdue, and the University of Wisconsin–Stevens Point—that phrase is opposed for a different reason: It’s a microaggression, allegedly.

“America is a melting pot” is still a widely accepted idea, one voiced by immigrants and natural-born citizens alike, by whites and minorities, ideologues and optimists. My partner, a Vietnamese refugee naturalized in the U.S., grew up with the idea of the “melting pot” even as she recognized that the Asian, black, and Latino communities in Los Angeles never “melted” with surrounding affluent white communities (and often not with one another). However inaccurate it is, “melting pot” is undeniably part of our glib national narrative.

The objection to this phrase, and to words like “stupid,” “rich,” “crazy,” “dumb,” “lame,” and “depressed,” is indicative of a problem with the social justice left (a group I routinely defend): a failure to distinguish between obviously bigoted language and common colloquialisms that most people don’t regard as offensive. While there may be good arguments for avoiding words like “dumb,” doing so warrants a very different pedagogical approach from acts of bigotry. Yet too often critics default to anger and scorn when people use such words, rather than seeing an opportunity for debate and education. In some ways, the controversy over politically correct speech is as much about how we choose to engage with one another as it is about free speech and silencing critics.

Granted, there’s no statute of limitations on a word’s offensiveness. The usages and contexts of the n-word, for example, have evolved in such a way that even its re-appropriation in black culture renders it anything but an anodyne word that’s available to all. Still, words like “lame” have evolved into usages far removed from their clinical or pseudo-clinical usages in the past. Similarly, phrases like “America is a melting pot,” like all clichés, carry no specific meaning, but rather acquire meaning in contexts ranging from benign to insidious. To rebuke someone for uttering these words—to set parameters of acceptability without discussing how and why those parameters come to be—is not only unproductive; it’s unjust.

That is, I take the castigation of someone for what they genuinely don’t know or can’t reasonably be expected to know as a justice issue unto itself, a problem related to what the philosopher Miranda Fricker calls the “epistemic injustice” of allowing prejudice to shape one’s impression of another’s credibility as a knower. Epistemic injustice may work in the other direction, too, in the bad-faith supposition that someone ought to know something is offensive when broader society has failed to treat it as such (therefore that person deserves to be shamed, scorned, or ridiculed for not knowing).