The case against therapuetic cloning
is effectively laid out by Dr. Charels Krauthammer in his Washington Post column today (free registration required, probably available elsewhere). Unlike President Bush, Krauthammer does not oppose embryonic stem cell research using embryos left-over from attempts at in vitro fertilization.
He draws his distinction based on the purpose for which the embryo was created. Extant embryos were created with the purpose of creating a baby and are therefore okay for research. Therapeutic cloning would use embryos created solely for the purpose of research (initially) and treatment (later) and Krauthammer finds that unacceptable:
The distinction comes down to the reason the embryo was created. Many distinctions in medical ethics come down to intent (e.g. is the morphine given to to end life or to relieve pain with the foreknowledge that it will stop breathing and end life?) and I am often skeptical.
But I deplore the step that proponents of such research are already demanding: research cloning, i.e., creating special embryos entirely for the purpose of using them for their parts.
Why, exactly, is it okay to experiment on human embryos and use them for parts if they were initially created as part of IVF (in vitro fertilization) and discarded as opposed to being created specifically for the purpose of curing disease and relieving suffering?
Aren't the "thousands of frozen and/or discarded embryos left over from work by in vitro fertilization clinics" troublesome to Krauthammer. Shouldn't we be a bit more careful about discarding human life and a bit more careful about how much we create?
I see the distinction, but to me either way you are doing research on what is, arguably, a human life. I see the potential benefits of such research as outweighing the downsides of creating and destroying life at such an early stage (the majority of "natural" embryos at this stage don't make it to birth), however the embryos. Krauthammer also doesn't address the fact that embryos created for therapeutic cloning may not be capable of ever progressing to humans (due to details of the process used to create them) than "left-over" embyros in fertility clinics. Some experts think technical obstacles to reproductive cloning may be insurmountable.
I've written much more here, here and here, and responded to what I consider less persuasive arguments against stem cell research here