I don't believe in cloning. There are certain people the world can do without multiple copies of. Me being on the top of the list. LOL.
No, on a serious note, can you picture a world where people live with themselves... Literally? A world where our clones are considered "unhuman"? Don't you think the clones would cause a revolt of some sort?
What if some A-hole decides to make a thousand clones of himself, start his own army and kills millions of people? Those are things you have to take in to consideration. That and nobody should be allowed to play God.