Donald Trump has said that he wants to ban anti-Semites, among others with disagreeable ideologies, from entrance into the United States.

It’s not a new idea. The United States banned communists and their sympathizers from entering the country. After World War II, Jewish groups wanted to ban Nazi sympathizers as well.

But there are reasons not to take the presidential candidate up on his offer.

First, it is un-American.

Here is what you have to do to become a naturalized American citizen.

I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty, of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same…

We might not like a whole host of beliefs that immigrants bring to this land — just as we certainly don’t like a whole host of beliefs that American citizens have.

But, instituting the thought police?

No, thanks.

Second, the notion of someone being “anti-Semitic.”

When I worked for the Anti-Defamation League, I learned a lesson from its then-director, Abraham Foxman.

Foxman warned ADL staff members to refrain from labeling people as anti-Semites. It is much more effective to label behaviors as anti-Semitic or bigoted.

Once you call someone an anti-Semite, you have effectively drawn a verbal gun — which will make it more difficult to educate someone away from their loathsome ideas.

There are glaring exceptions to this rule. But, in general, Mr. Foxman’s advice still holds.

Anti-Semitism is a constellation of ideas, attitudes, mythologies, worldviews and beliefs. All of those ideas are problematic.

They move from problematic to really problematic when the holders of those beliefs choose to act on them.

In other words: I really don’t care what you believe. But, if you act on your beliefs in a way that endangers common decency and public safety — then, we have a problem.

There is a third reason why we shouldn’t be policing anti-Semitic beliefs.

Because, a whole lot of people have those beliefs.

Consider how widespread anti-Semitic beliefs already are in this country. (My source — Daniel Jonah Goldhagen’s The Devil That Never Dies). For example:

• About 30 percent of Americans believe that Jews were responsible for the killing of Jesus.
• 20 percent of Americans believe that Jews have too much power in the business world.
• 30 percent of Americans believe that Jews are more loyal to Israel than they are to the United States.

You realize, of course, how many Americans are accounted for in these numbers. We are talking about millions of Americans who have such beliefs. On any given day, you interact with many people who believe any or all of these canards. But you don’t know this because, thankfully, they neither speak about their beliefs nor act upon them.

Like I said: Believe what you want. Just don’t get in my face about it.

What about Europe?

According to Goldhagen, anti-Semitic beliefs are far more entrenched in European society than in the U.S. It is fair to say that many European immigrants probably hold anti-Semitic views.

What about Hispanics born outside the United States? Also, a high level of anti-Semitic views. That would include Catholic Hispanics whose churches have not exactly gotten with the “Nostra Aetate program,” and whose priests still teach that Jews are responsible for the killing of Jesus.

If you throw in immigrants from the Middle East, more than a handful will have anti-Semitic beliefs.

That’s the bad news.

Here is the good news.

As Goldhagen writes, the rate of anti-Semitism among American-born Hispanics is half the rate as it is among those born in foreign countries.

Exposure to American mores and society — not to mention, real live Jews — can actually help heal anti-Semitism.

Moreover, immigrants from the Middle East — who might also have anti-Semitic beliefs — have demonstrated their eagerness to assimilate to American values — which could mean the possibility of lessening anti-Semitism.

To hope that this might be true, and to work toward making this true — is this not the hope of America itself?