Jim Henley weighs in:
Caplan makes the same (offensive) mistake that many human-cloning opponents make: not fully recognizing that a cloned child would be its own person, as human as you or me, as like and as different. I never agreed with the cloning prohibitionists and I don’t now. But I always counted on them having the creepier end of the argument.
A reader adds:
Perhaps this should go without saying, but an individual's clone will *not* be exactly like that individual, even if the clone is a perfect genetic copy. We already have such people - perfect genetic copies of each other - all over the place. They're called identical twins.
As any of us who have gotten to know identical twins can tell you, though they look and sound incredibly similar, they're different people. Different tastes, different ambitions, different views. There is a lot of evidence that identical twins, even ones separated at birth, share a lot of character traits or propensities. But even then, even at a biological level, they're different people.
The expression of a trait, phenotype, is a different beast than the coding of that trait in genes, or genotype. The trait in question, whatever it is, must be translated from the genetic code and expressed. Differences in environment, even for identical twins raised in the same home by the same parents, do exist on a "micro" level and will be reflected, however slightly, in the phenotypic expression of the otherwise exactly similar genetic codes shared by these twins.
This is why, when Caplan says, "I'm confident that he'd be delighted, too, because I would love to be raised by me", he reveals that he doesn't understand what he's talking about. Caplan wouldn't be raising a doppelganger, but a much younger identical twin with its own agency and with a slightly different phenotypic expression of the same genes. His "mini-me", if you will, might not have any his tastes or views at all, and might very well dislike being raised by "himself".
The area of study the reader is referring to is called epigenetics. The NOVA episode previewed above can be seen in three parts - here, here, and here.