Samuel Huntington argued in his book “Who Are We?” that Hispanic immigrants were a threat to the national identity of the U.S. because, unlike other ethnic groups, they were not assimilating into the host nation. The news that Univisión Communications, the Spanish-language media conglomerate, is up for sale is one more indication of how wrong this well-respected gentleman is. Univisión controls more than 80 percent of the Spanish-language market but second generation Hispanics prefer English programming and therefore its long-term prospects for growth are small—unless it too assimilates.

There appears to be no reason why owner Jerrold Perenchio should sell. His conglomerate, which includes T.V., radio and music, is a money-making machine. In 1992, Mr. Perenchio bought Univisión for $500 million; today, the media conglomerate has a market capitalization of $10 billion.

However, the demographics are not working in favor of Univisión. Births are outpacing immigration as the key factor in the growth of the Hispanic population in the U.S.. The Hispanic market continues to grow strongly, but native-born Hispanic Americans, rather than new immigrants, are the real force behind this expansion. And—you guessed it—second generation Hispanics speak English and to an increasing extent prefer to read and watch English-language media.

Anyone who is remotely familiar with the Hispanic market has known this for quite a while. I had first-hand experience myself when I worked for a newspaper chain in Florida some years ago. Studies by organizations such as Pew Research Center, the Urban Institute, and Kaiser Family Foundation indicate that American-born Latinos now represent 60 percent of all Latinos; that the second generation is bilingual, has a higher level of education and earns more money than their immigrant parents; and that the third generation doesn’t even speak Spanish. If anything, the stigma that being an immigrant carries in the U.S. nowadays will push the second generation to emphasize their American condition. And newcomers cannot stop that process. In fact, their children will do the same.

For further evidence that American-born Hispanics are assimilating, just look at the numbers of conversions to Protestantism: one quarter of all Hispanics declare themselves Protestant (40 percent of those even call themselves “born again”). Of course, this is a dubious measure of change because Catholicism has been the principal Christian denomination in the U.S. since the second half of the 19th century!

Mr. Perenchio may have other reasons to sell (say, retiring to Bora-Bora to chase mosquitoes), but it is obvious that the television network, which mainly caters to first-generation Hispanics with voluptuous soap operas, cannot continue to expand in any major way unless it does something drastic. Introducing bilingual programming, for example, might expand Univision’s audience, but it also runs the risk of alienating its first-generation base. The challenge posed by a second generation that has turned away from the Spanish-language media—and not just competition for new electronic media—may be the reason why the network’s advertising revenue has recently been growing at about one third the rate of T.V. revenue in general.

Young, English-speaking Hispanics would rather watch reality shows like “The Real World’ and comedies like “George Lopez,” as a recent story in the New York Times pointed out, or listen to “Hurban” radio, a musical hybrid with which Clear Channel is now experimenting.

Of course, no group assimilates without impacting the host culture. But that has been the history of the United States. Every religious or ethnic group that became part of the U.S. nation enriched it without fundamentally altering the basic ideas that inform its institutions. Yes, Hispanics will influence U.S. culture, but it is also true that the prevailing culture, starting with the language, is influencing them a lot more! Many Hispanics appear to want to see their stories reflected in T.V. programming in English. I would be surprised if English-language T.V. networks did not factor that into their future plans. But those stories will be in English and will show Hispanics in the process of assimilating!

Hispanics are not a threat to the identity of the nation. They are a confirmation that there is no such thing as one “national identity” in the U.S.—i.e. an identity that one group imposes on every other group. There is, rather, a flexible, porous culture that continually adopts new shapes within a basic set of institutions made up of liberal democracy, private enterprise, and the rule of law. Like other immigrant groups before them, Hispanics seem to be adapting to that creed while at the same time adding new layers to the complex prevailing culture.

Only sclerotic cultures are destined to die, Mr. Perenchio’s business notwithstanding.