Julian Baggini has offered an interesting explanation for our phobia of clones. He suggests that we each assume we have a pretty good idea of who we are. But clones of ourselves threaten that assumption because
No matter how scientifically suspect the idea is, we think of clones as duplicates of selves. Since they are not unique, not completely free, and offer a very different perspective on who we are, they threaten all these day-to-day certainties.