Cloning is the process of taking genetic information (DNA) from the cells of an organism and placing the DNA into another cell, thereby hopefully causing that cell to form into a copy of the original organism. This can be done naturally (i.e., twins) or using technology with plants and animals. Now, however, the technology is being applied to humans and this raises the ethics of the procedure.
Cloning in the plant realm occurs naturally. For example, potatoes, which grow as roots underground, can be removed from the original plant and replanted elsewhere with the result of the new plants being identical in form and taste to the original. There are grasses that send out shoots underground that form other identical plants.
There are insects that can reproduce asexually, a type of cloning method where the insect uses the existing genetic information without the aid of an opposite sex. The asexual reproduction is a continuance of existing genetic information which then produces identical offspring to the "parent."
Occasionally, animals and humans are born as twins. Twins can be identical in genetic makeup since the initial zygote (fertilized egg) splits in such a way as to make an identical copy of itself which then matures along with the other(s) to form babies.
So, we can see that cloning occurs naturally. But does this mean that we are to apply the technology to cloning humans?
But what about people?
Biblically, there is a great distinction between animals and people. We are made in the image of God (Gen. 1:26) where animals are not. We are commanded not to murder humans (Ex. 20:13), yet we are told to kill animals for food. This means that humanity is substantially different in nature than the animal kingdom. The evolutionist, however, sees little difference between animals and humans except to say that we are more advanced biologically due to evolution (an unbiblical theory). Therefore, ethically, the evolutionist would be more inclined to participate in human cloning research since biblical concerns are not relevant. This is a problem because it opens the door for all sorts of atrocities. What is to prevent a cloned human from being killed in order to harvest his organs? If the clone is considered fully human, then hopefully secular ethics would prevent murder. But we cannot say. And, if someone wants to say that scientists will be ethical, then just look at history. Being a scientist is no guarantee of ethics.
For Christians, this comes down to God's created order that we marry and produce children through His ordained means of procreation. Human cloning goes against this and risks the manipulation and murder of another human life. Therefore, the cloning of full human beings would be wrong since it rebels against God's created order of having a mother and a father, of using the God-ordained procreative means, and it usurps God's sovereign right to be the author of the life in the womb.