Technical questions aside, the real reason that we've never cloned a human, according to George Annas, a bioethicist at Boston University, is that there's no point.
In most countries there are laws or agreements against artificially creating a genetic duplicate of another person, both because of ethical concerns and technical difficulties. Cloning is still far from a perfect science, and creating an imperfect clone would likely mean making a person with potentially devastating genetic abnormalities.
While we can read an entire human genome — and the technology we use to do so continues to get faster and cheaper — we still have no idea what a lot of it really means, or how it codes for traits and behavior.
But even if we knew that we could successfully copy the exact genetic code of another person without making errors, Annas asks: "Why would you want to duplicate a human?"
"Nobody's got a perfect genome," he explains, and there's no reason to make a copy of all of someone's imperfections and disorders.
Just because cloning humans is not a good idea doesn't mean no one will ever do it. Some people might devise some reason to try and clone a person, imperfections and all — to use them for a research study that reveals the difference between nature and nurture, or to raise a copy of their favorite actor or artist. But these aren't really good reasons to make a genetic copy of a person, and they're rather unethical as well.
Making a genetically modified human instead of an exact clone of an existing one could be a different story.
