
Simply put, cloning just makes sense.
The state we are currently in is one where transplanted organs must come from freshly dead cadavers or artificial sources, or in some cases, animal organs like pig hearts. The one consistent factor between all of these options is that they are not reliable.
Those who oppose cloning often make the argument that killing is not okay, and that creating a clone to be harvested for organs is unethical because it involves killing a human being. The alternative to this is to let people with faulty organs die slowly on life support, or use faulty organs that will require heavy medication to allow the body to accept the transplant. Does this sound ethical to you? I don't think it does.
The bottom line is this: When someone's vital organ fails, someone IS going to die. Were a clone to be raised to produce a better organ replacement, it would be that clone. Consider the two options: Kill a person who has already lived a long life and has a lot to offer humanity, or a clone which has nothing to offer besides its organs.
The choice, to me, seems obvious.