Despite a recent reversal in the immigration trend, Hispanic people are still the most dominant minority in the U.S. They are everywhere, and it makes some people fear that English will lose its de facto official language status. To counteract that, some people want to make a law or a constitutional amendment making English the official language of the land.
This is a terrible idea. Once such a law is enacted, the state's control over the minutiae of everyday landguage can become extremely invasive. If you want a prime example of that, just look at the Canadian province of Quebec, whose French language is "protected" by its infamous language laws (Loi 101 in French). These laws make it extremely difficult for businesses to operate in the province, as the Economist recently demonstrated.
For example, if a corporation wants to open a shop in Quebec, it either has to translate its name to French or adopt French words in its title (such as "magasin"). It may look like a petty detail, but if the Office québécois de la langue française (OQLF, often referred to as the language police) wins an ongoing court battle, then shops like Walmart, Old Navy, and Target will have to put a French twist to their names, and they will have to bear the cost. If not, they could be fined up to $20,000 or be denied their entire existence, as this young entrepreneur shows. This means that new shops might think twice before going to la Belle province, which could eventually lead to higher prices because of the lack of competition.
This French obsession does not stop here. An Italian restaurant in Montreal (which prompted the so-called pastagate) and another one in Quebec City were both compelled to change their menus and lettering (at their own expense, of course) because they didn't have enough French. Even ice cream shops are not immune from language police visits, who can come whenever people complain about violations in the Loi 101.
As if it weren't enough, the Quebec government also obligates businesses with more than 50 employees — there is a proposed bill that would lower this number to 25 — to function mainly in French, be it amongst employees or with customers (requiring a French certification), with all the costs that such a transition may imply. In other words, businesses will now have an incentive not to grow too much in order not to comply with these restrictive laws, just like France's 50 employees law that has created 2.4 times more businesses with 49 employees in order to avoid stifling regulations. It will be seen that businesses now function in French, but it will be unseen that many won't grow beyond 50 employees (or won't be created at all).
So if you want your government to be so intrusive as to dictate private businesses in which language their signs must be and in what size, which language must be spoken with clients and employees, which school your children can attend, and count on 1984-style citizen denunciation of dissenting companies, then the U.S. must definitely adopt English as the official language of the land.
But if you believe that consensual relations should be left alone, notwithstanding the language it is in, then oppose language laws with all your energy. Besides, it would be quite useless in the U.S.; English is the de facto language of the land, and people who want to have a chance learn the language. Droves of non-English speaking immigrants in the 19th century hasn't change that, and massive Hispanic migration is unlikely to do it either, if my in-laws are any indication — second-generation people in the U.S. all speak Spanish with an accent and English among themselves, and those who have children barely speak Spanish to them.