Cloning is as immoral as in vitro fertilization since it, too, separates the unitive (love) and procreative (life) faculties from married sexuality.
It is not even sexual reproduction by biological duplication. The dangers of creating a race of clones that might dominate the earth is the stuff of science fiction, but the real potential for the manufacturing and distribution of clones to harvest spare body parts is macabre at best and grossly immoral at worst.
Just because science can do something does not make it morally permissible to actually do it. Genes, chromosomes, and DNA are potentially alterable, but we do not know the impact and long-term effects of tinkering with the genetic code of life itself.
The Sacred Congregation for the Doctrine of the Faith issued a document in 1987 entitled Donum Vitae (Gift of Life) which reminded Catholics not to take human life for granted and that each and every human life is a gift from God, not a product to be made or manipulated.