Heinlein's view of cloning wasn't very well developed, and it's fair to criticize his use of sexuality to market his writing. The secularism of the mid-20th century carried with it a gross potential to dehumanize us by undermining the precious uniqueness of each human being, and Heinlein didn't seem to notice the pitfall. Christian anti-communists such as Pope John Paul II understood that abortion, cloning, genetic research, and cyborging were all extremely dangerous to our future. There are science fiction authors who have treated these themes. Even Asimov's discussion of robot rights and obligations begins to account for the nature of sentient beings. I consider Mamoru Oshii's Ghost in the Shell series to be one of the best hard-scifi treatments of cybernetics gone mad, and they far outstrip Heinlein's naive perspectives.
Francis Fukuyama has treated some of these issues in his book
Our Posthuman Future: Consequences of the Biotechnology Revolution. New York: Farrar, Straus, and Giroux, 2002; Picador, 2003 (paperback).