What if China, flush with its new wealth, opened its doors to mass immigration? It would make sense from an economic and social point of view, because its one-child policy has produced a young generation far smaller than the one that now does most of the work. China's population is ageing faster than any other country in history, and it could certainly do with some more young people.
If it had an immigration policy like that of the US, it could fill the gaping holes in the workforce that will open up when the present generation retires.
So let's suppose China opens the gates. The immigrants would come, from all over the world, and China would be transformed. In 50 or 60 years, it would be one of the world's most diverse societies. Almost all the new immigrants would learn to speak some Chinese, of course, but their children would be fluent. Indeed, they would think of themselves as Chinese, even though their skins were white, brown or black and their religions Muslim, Christian, Buddhist or Hindu.
Some tens of millions of them would already have intermarried with ethnic Chinese. And everybody would live more or less happily ever after.
It's never going to happen, because the Chinese would never let it. But that's the point. The Americans have let it happen. Why? It is an extraordinary thing. Sixty years ago, the US was a country whose population was overwhelmingly of white European descent. The only really big minority was the black and mixed-race descendants of African slaves, who accounted for about one-eighth of the population. And then the US opened the gates very wide.
Last month, the US Census Bureau revealed that non-white births in the country narrowly exceeded the number of births to white Americans for the first time. There are some curious kinks in the statistics, but the message is clear: the next adult generation in the US will not be majority white.
So why did the last two generations of Americans, who were still mostly of European descent, let it happen? Did they welcome it as a good thing for the country's future? Or were they just asleep at the wheel?
One plausible explanation is that it was about fairness. As descendants of immigrants themselves, they felt that they could not deny others the same opportunities. Many older white Americans were clearly uneasy about the new social reality, but most remained true to their ideals and never mobilised to stop it.
Maybe the last two generations of Americans were a lot less racist than many people thought. Or perhaps they were all silently aware that, only 500 years ago, none of the babies born in North America were white.
Gwynne Dyer is a London-based independent journalist