A little over a year ago, Facebook decided to expand beyond college and high school students. At the time, the planned change was met with stiff opposition from many users. The rationale, despite Facebook’s relatively stringent privacy settings, ranged from fear of curious parents to fear of creepy child molesters.

Cooler heads prevailed, and now these concerns have largely vanished. To some, this is no surprise. At the time of the controversy, a Facebook spokeswoman prophetically pointed out, “Whenever we’ve opened up our network, our existing members have reacted negatively, even though they’ve always adjusted.” This quote illuminates the underlying reason behind the opposition to the expansion: No one wants to be part of something that anyone can be part of.

This point applies precisely to United States immigration history: Whenever the U.S. has opened itself to more immigrants, much of the country’s current population has been unhappy. In the 1850s, Irish immigrants faced hostility, particularly among Protestants afraid that Irish Catholics didn’t share their values. Seven decades later, the Immigration Act of 1924 sought to squelch the rise of Southern and Eastern Europeans migrating to the U.S.

Although the creeds and origins of potential immigrants have changed over time, the cultural argument for opposing their migration has stayed remarkably constant. Inevitably, one of the main claims against immigration is that the would-be countrymen won’t assimilate into the so-called American “melting pot.”

And so we come to the current debate on immigration, which is ostensibly only about the illegal kind. However, modern opponents of illegal immigration trot out the same tired argument—in a slightly different form—which involves some vague notion of culture, and an equally vague idea that illegal Mexican immigrants won’t fit into it. (This begs the question: Why won’t illegal immigrants fit in, but legal immigrants will?) Although the suggestion that there is a monolithic American culture sounds nice, it is more fallacy than fact. The beauty of our country isn’t its (non-existent) singular culture, but rather its many different ones.

To those who disagree, I would ask: What, precisely, is “American culture?” Apple pie and baseball? Certainly, you could compare America to other countries and argue that, for example, Americans are much more religious than the French, or more competitive than the Chinese, or more freedom-loving than Iraqis. These things—along with a number of other generalizations—might be true on balance, yet they don’t demonstrate a particular culture. In the same way that we shouldn’t generalize based on race, we shouldn’t generalize from nation to nation.

In reality, our shared culture begins and ends with the English language—it’s the only real thing almost all Americans have in common.

This brings up another common cultural argument against illegal immigrants: Some don’t speak English. In this respect, Mexican immigrants are not historically unique. Many immigrants to the U.S. didn’t speak English when they came, but all of them had a strong incentive to learn. In fact, many of them—and all of their children—did. There’s no reason to think that recent immigrants (illegal or otherwise) will be any different.

Perhaps there are legitimate arguments against illegal immigrants—such as simple fairness, or their effect on the economy—but their influence on our culture is not one of them.

The cultural rationale for less immigration is simply rationalization. But why do people embrace these ideas? It’s the same reason that Facebook members didn’t want the site to expand. And it’s the inherent tension in human nature: We want to fit in—but not to well. We want to be part of a something bigger than ourselves, but we don’t want to be part of a mob. We also want to be unique and independent, but we don’t want to be alone. We want to be part of a great country, but once we’re part of it, we try to keep others out. This desire for exclusivity is part of human nature. But another part of our nature is exploring—and sometimes, ultimately, rejecting—our assumptions, prejudices, and preconceived notions.

So what’s the lesson from Facebook? It’s that no matter our feelings now, we Americans will always adjust, at least culturally, to new levels and new types of immigration.