“Microaggression” is a trendy, modern word for insensitivity. It means saying things that inadvertently make some people feel excluded or the targets of subtle bias. It is good to be sensitive, and it is good to make people feel included. Everyone, in an ideal society, should be conscientious of other people’s feelings and empathetic to other people’s experiences. For professors, who are in positions of authority over young people, this kind of consideration is especially important.

But the University of California’s new faculty training guide goes way too far in its attempt to train professors to be sensitive. Most of the statements it encourages professors to avoid definitely are insensitive and should be avoided. But a couple of them actually are true — and not just true but important and valuable things young Americans should know. When we start proscribing, saying things that are true and important in the classroom, we have left the realm of sensitivity and consideration.

For example, the guide encourages professors not to say “America is a melting pot.” This, according to the guide, will put unacceptable social pressure on minorities to assimilate into the dominant culture.

Now, I believe assimilation is a choice — you should assimilate as much or as little as you want. But regardless of what I believe, or what anyone else believes, the pure and simple fact is that the U.S. does enjoy a very high degree of assimilation. The numbers overwhelmingly back this up. Immigrants to the U.S. adopt the local language and local customs at an astonishingly rapid rate. A 2010 report by the Center for American Progress, a liberal think tank, looks at a large array of data and concludes the following:

“[W]e use the most comprehensive U.S. Census Bureau survey data to investigate how well the [assimilation] process is working for today’s immigrants. Replacing the misleading rhetoric of immigration opponents with firm data, this study shows that assimilation is happening across our nation. …[O]nce we examine immigrants’ advancement over time — in this study from 1990 to the present — we discover that the longer immigrants are here the more they advance and the better they are integrated into our society.”

The CAP study shows that immigrants adopt the local language, spread out across the country, advance in terms of education and income, become citizens and buy homes. This is true across all racial and national immigrant groups. Other studies, looking at historical parallels, find the speed of immigrant assimilation was true in past waves of immigration as well.

So America is a melting pot. Whatever your personal opinion of assimilation, it is an objective fact.

Another thing the UC faculty training guide wants professors not to say is that “America is the land of opportunity.” Now, we could quibble over the word “the” — obviously there are other lands where opportunity is as great, or possibly even greater. And by now it is common knowledge that U.S. relative income mobility is lower than that of many European countries.

But the simple reality is that the U.S. has a very high level of economic opportunity for immigrants. Economists Karthik Athreya and Jesse Romero looked at the data in a 2012 report. They found immigrants to the U.S. tend to dramatically increase their earnings relative to what they earned in their old countries. Immigrants also tend to catch up to the native-born average, though this tendency has decreased a bit in recent years.

The data in the CAP report, which I mentioned earlier, also are strong evidence the U.S. is a land of opportunity for immigrants. The children and grandchildren of immigrants tend to catch up to native-born levels of homeownership and educational attainment — important measurements of opportunity that may not be fully captured by income statistics.

So, saying “America is the land of opportunity,” while open to dispute, certainly captures several very important facts about the country.

I believe it is important to allow professors to say true and relevant things in the classroom. This should take precedence over the need to prevent microaggressions — especially because these statements may not even be microaggressions in the vast majority of cases, the people who write faculty training guides are not perfectly informed.

But beyond the pure concern for truth and facts, there is another reason I think these particular expressions shouldn’t be discouraged. As I see it, the ability to assimilate immigrants is one of the fundamental strengths — perhaps the defining strength — of the U.S. as a nation-state. Assimilation — not complete, not perfect assimilation but some substantial degree of it — is what has saved the country from suffering the racial, ethnic and religious tensions and conflicts that have plagued more homogeneous societies in Europe and Japan. The forging of a national, common American identity is absolutely crucial to ensuring a functioning society, good government and a strong commitment to providing public goods. If we allow well-meaning censors to make assimilation a taboo, I believe our continued prosperity as a nation is in jeopardy.

Let’s remove these items from the list of discouraged microaggressions. The U.S. is a melting pot. It is a land of opportunity for immigrants. And for my part, I hope it remains both these things.

Noah Smith is an assistant professor of finance at Stony Brook University and a freelance writer for finance and business publications. He wrote this OpEd for Bloomberg View.