Here's something every human geneticist or livestock breeder knows: You need to freshen up your gene pool, or your population will be plagued with all sorts of weaknesses and genetic disorders.
Americans once knew we were meant to be a nation of immigrants, which is why we welcomed so many. As a result, we became the strongest nation on Earth, intellectually and socially, and long before militarily. Yes, we screwed up and discriminated against persons of color, and we treated most newcomers as second-class citizens, though in fact, we were all running away from somewhere.
We sometimes forget that those who came on the Mayflower, whose descendants today act like American nobility, were actually a bunch of scruffy religious nuts who didn't fit in.
However, we also tend to be a nation of hypocrites, who think immigration was great until after our ancestors finally arrived.
After that, of course, we needed to severely limit it. Imagine what today's politicians would have thought of a 9-year-old Jewish boy just arrived from Russia — dirty, poor, not able to speak a word of English, with a father dying of consumption.
The boy, David Sarnoff, got off his boat in 1900. He went on to establish radio as a broadcast medium, created RCA and NBC, hired teams of engineers to create television, and then color television. Before he died in 1971, he predicted fiber-optic cable.
Back then, pretty much everybody without a violently contagious disease could come to United States. We've made it much harder now. Some sneak in, and bashing illegal immigrants has become almost as popular among bellowing right-wing radio hosts as bashing mythical welfare queens was, back in the day.
The fact is that the best thing that could happen to Detroit would be a vast influx of immigrants to rebuild the city and create jobs, which is what immigrants tend to do.
Yes, some are or become criminals, just as some unhappy young white men shoot presidents and Beatles and children in schools.
And my guess is that, statistically speaking, immigrants have a much better track record than most of us.
We used to know that. We were proudly taught in school that we were a nation of immigrants. That's back when we were confident about ourselves as a nation, something we seem to have lost.
Some of this is due to the disgraceful and ignorant racist Donald Trump, who has profaned the presidency in so many ways, including being profoundly anti-American about immigration.
Until recently, Trump's attitude wasn't typical in the party he's hijacked. Republican businessmen have been some of the strongest supporters of immigration. Governor Rick Snyder, in fact, asked the federal government to set aside 50,000 EB-2 visas to allow skilled immigrants from anywhere to come build up Detroit.
That didn't happen, but it was an excellent idea.
But now irrational xenophobia and hatred seem to be part of the Republican platform. Brian Dickerson, the editorial page editor of the Detroit Free Press, pointed this out in a recent insightful column.
He noted that a bipartisan majority in the U.S. Senate was ready to pass a deal that would have allowed the dreamers to stay, while setting aside $25 billion of extra border security.
But the Republican hardliners rejected it, as Dickerson noted, "mainly because it ignored Trump's demands for new restrictions on legal immigration." Essentially, that means Aryans good (especially Norwegians); people of color (especially Muslims) bad.
Immigrant bashing is something that has ebbed and flowed throughout American history, at least as far back as the Know-Nothing Party in the 1850s. And while Trump seems especially appalling, perhaps because he makes virtually no attempt to conceal what he is, he has plenty of help, and on this point, many Americans, normally the most welcoming of people, are confused.
Consider this poignant story that illustrates how screwed up our thinking on immigration has become:
For some years, I've worked with a brilliant, charismatic and very successful development executive to help her raise money for a worthy nonprofit I support. I originally thought she was Chinese, with perhaps some African-American thrown in.
But eventually, she told me she was Korean, born in Seoul, but adopted by a soldier from blue-collar Roseville. She was in line to get a top post in a Korean-American organization when her father, who raised her as a single parent, said they needed to talk.
"I did things in Vietnam nobody knows about," he told her. She was confused. "You mean Korea, right? You weren't in Vietnam."
"Vietnam," her father said.
But, she pointed out, he hadn't even been sent overseas till after Saigon had fallen and the last Americans left Vietnam.
"That's right," he said. But we were still running special clandestine intelligence teams into the country. One day, sneaking across a rice paddy, her dad heard what he thought was the piteous cry of a Vietnamese pygmy goat. But it wasn't a goat.
It was a very sick and abandoned almost newborn baby. His commanding officer told him to leave it there.
The soldier refused, risking court-martial. Somehow he got it back to the base and to a hospital, which confirmed that the baby was very, very sick.
My friend listened, stunned.
"Did the baby live?" she asked.
"You might say that," her father said. "She became you."
Odds are that some Vietnamese woman was impregnated by an African-American soldier. Having such a baby might not have been a good thing in the first years after the end of the Vietnam War.
Life is not, however, a Hallmark movie, and the story doesn't end there. My friend's father did a wonderful job raising her, but she hasn't spoken to her dad for more than a year... because he voted for Trump. "He resented all the immigrants with the special visas taking American jobs," she told me quietly.
In fact, those immigrants create far more jobs than they take, which he evidently didn't understand. It's hard to imagine her father voting for the creature who has polluted the White House.
But people are a bundle of contradictions, and when that young soldier plucked that baby out of the water, he was a better American than Donald Trump will ever be. What we need are leaders who would remind all of us what America is supposed to stand for, and what Lincoln called "the better angels of our nature."
Interesting twist on mass murder: Anyone who has followed my writing knows that I have no use whatever for guns. I think we should require any privately owned weapons to be kept locked up at a shooting range or a hunting lodge.
But Harry Frank, a retired professor of social psychology and one gun enthusiast I respect, offered me a very interesting take on the demand we outlaw military assault-type weapons, like the one used to kill 17 people in the recent Parkland, Fla., school massacre.
"According to the FBI, there were 15,070 homicides in 2016," he tells me. Of these, he learned that 374 were committed using rifles of all kinds, while there were over 7,000 handgun homicides.
"I find it interesting that the victims of much publicized (but extremely rare) mass shootings involving assault rifles were white, whereas the victims of handgun shootings continue to be largely inner-city persons of color," Frank notes.
That may not say much about violence.
But it may speak volumes about media priorities.