"Diversity is a social construction that can be deconstructed and reconstructed - you can erase a line and draw a new line [to define identity] and we do it all the time," says Putnam, who adds that there has been much more response to his research in the UK than in the US.
"Some critics [in the UK] on the right say that's all hogwash. What gets the conservatives irritated is that I say the task is not to 'make them like us' but to create a new 'we' - a new, more encompassing identity. They say: 'Why should we? We don't want a new we, we like the old we.' But in the US, we don't have that problem because we have changed in the past," he says.
America IS a nation of immigrants. Britain has not been - the 'nation of immigrants' nonsense is a liberal myth used to justify mass immigration.
Up until 7/7 our new liberal rulers didn't care about integration. The USP of immigrants was precisely the fact that they 'weren't like us' i.e. the natives. What they actually were like was unimportant.
Now they've seen the writing on the wall in Tavistock Square.
So integration seems like a good idea after all.
The trouble is that the destruction of British culture was a prerequisite for mass immigration - a self-confident nation would either not have allowed it or would have ensured integration was a priority - which was what happened in America until very recently.
The continuing effort to reinvent a national identity should at least provide sour amusement for a few decades.
Back to Mr Putnam. The key driver for the British cultural revolution - and the Britain we see today - was the decline of Christianity.
He credits religion with a vital role in spurring on progressive change in the US over the past 150 years - contrary to popular European wisdom, religion has predominantly been a force for good in America and its current use by the political right is an aberration from its history, he argues.
"Religious revival has been an essential ingredient of every progressive movement: the abolition of slavery came out of the second great awakening; the progressive era of 1900-15 when the US first passed labour and environment legislation came out of the social gospel movement," says Putnam, who is a convert to Judaism.
Much of his book will be devoted to analysing how that progressive potential in religion was lured to the Republican right. It is easy to see how his interest in social capital and religion fit together, but he is quick to acknowledge that religion can also have detrimental consequences, and it is possible to have social capital that has no religious underpinning.
He strikes a warning on the secularisation of Europe, which he describes as the first large-scale effort to see whether secular progressive countries can reproduce themselves and successfully pass on the values on which they were built. "I believe they can," he says, "but the evidence is not yet in. Europe is still living off its religious heritage."
Christianity may be dying in Euruope, but Nature abhors a spiritual vacuum. I notice a continual drip of British Muslim converts. They may be misguided, but they are generally intelligent, well-meaning young men and women. The canaries in the coal mine ?
"I am a white, middle-class left-wing atheist, who embraced Islam, and I see it has having the solutions to all the social ills of British society (poverty, drug abuse, gambling addictions, robbery, individualism, depression and terrorism, amongst many others"
I'll pass on whether there are no poor people in Muslim countries - but for the rest, you could say much the same of the Christianity that was - before the churches turned into a branch of Social Services.
Maybe the Sixties cultural revolutionaries who are dying off, the George Melly's, won't see their new Utopia.
"And always keep a-hold of Nurse
For fear of finding something worse."