My sister and I are both anime fans, and recently we watched Ghost in the Shell: Stand Alone Complex, an excellent science fiction series that deals with the societal effects of huge advances in artificial intelligence and the widespread use of synthetic bodies and brains. In the thirteenth episode, a girl is suspected to be a clone of a kidnapped CEO's daughter. While we were watching, my sister asked me an interesting question: A clone wouldn't have a soul, she said, so what would it act like? She seemed genuinely stumped by the question. I couldn't just tell her that there's no such thing as a soul, so I said, "That's hard for me to answer. You should take some philosophy classes."
Both of those statements were technically true. Nevertheless, the question does deserve an answer. Basically, a human clone would be nothing more than an identical twin of the original person (albeit one born at a later date). They would probably behave at least somewhat similarly to the original, since they would share the original's genetic code. However, they would certainly have differences in personality, since they would grow up in a completely different environment.
Human cloning is one of the many issues that highlights the problems with the Christian conception of the soul. There doesn't seem to be anything in particular that would distinguish humans who do and don't have souls—in other words, the idea of a "soul" is useless; it explains nothing that can't be explained by natural means. According to Occam's razor, souls would qualify as "unnecessary entities," and so we have no reason to incorporate them into our worldview.
The view that a human clone wouldn't have a soul is actually a fairly common one, and the Bible is even cited in support of it. In Genesis 2:7, it says:
"And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living being."
Since it seems that in the Bible God personally imbues man with a soul, many Christians believe that a man-made clone wouldn't have one. In fact, some predict that creating a live human clone will be impossible, and will instead result in a lifeless body. Once or twice I've also heard the pastor of my church make a very startling claim: if living clones are produced, they will only appear to be "alive" because the bodies are inhabited by demons. I can easily envision a future in which clones are persecuted or even killed by a faction of extreme fundamentalist Christians. After all, if clones are merely lifeless, demon-possessed puppets, to "kill" them would be a perfectly acceptable (perhaps even commendable) act according to a Christian worldview.
And if many years from now people have their minds uploaded into artificial brains as in Ghost in the Shell, I suspect that many Christians wouldn't believe that the soul would be transferred. They might apply the same explanation of demon possession to living bodies containing mind uploads. Thus, the potential harm that Christianity poses is not limited to present issues such as gay marriage and stem cell research. As technology opens up new paradigms, it may actually create opportunities for the most fanatical Christians to kill innocent people.