Although nearly everyone in favour of therapeutic cloning swears that reproductive cloning is unethical and unsafe, very few are able to explain exactly why it is unethical. Now an American law professor argues vigorously in a new book that cloning should be legalised. Kerry Lynn Macintosh, of Santa Clara University, in California, says that a ban violates the US constitution and that fear of cloning is irrational. The most quoted bioethicist in the US, Arthur Caplan, praises as "a courageous and important book".

If a ban is such a mistake, Caplan asks how cloning could have become "one of the most widely outlawed activities on the planet". He identifies abortion politics as the answer. Outlawing cloning, he says, is a backdoor way for pro-life activists to push for granting human embryos full legal rights from the moment of conception.