These adult stem cells are multipotent: they have the ability to turn into a variety of types of tissues. Successful stem cell therapies cause the DNA in the adult stem cells to further differentiate into more specific types of cells. There is no point in getting the adult stem cell to turn into a less differentiated type of cell, or using the more primitive embryonic stem cells. This would be going backward, in the opposite direction of providing a clinically useful therapy.
The first two sentences there are OK (sort of; it's not really the DNA that differentiates), but the latter two are dubious in the extreme. It is true that "adult stem cells" are more differentiated than "embryonic stem cells". But this means that the utility of adult stem cells is more limited than that of their embryonic counterparts. Because adult stem cells have already partially differentiated, they can only be induced to develop further along the paths they've already started down. Thus, if you want to induce an adult stem cell to become a nerve cell, you've got to find an adult stem cell that hasn't already diverged from the developmental pathway that leads toward nerve cells. If you can't find such cells, you're out of luck. By contrast, embryonic stem cells are completely undifferentiated and can in principle be induced to develop into any kind of tissue. Hence, the potential for treatment is unlimited; with embryonic stem cells, there are no theoretical limits on what sort of tissues can be accessed.
Of course, I don't want you to get the wrong idea about where I stand here. For one, you've undoubtedly noticed the presence of both "in principle" and "theoretically" in my brief discussion of embryonic stem cells. This isn't a mistake or even a hedge; it's simply the state of things. The author of that American Thinker piece is absolutely correct when she notess that no medical treatment based on embryonic stem cells is currently available (or even in human trials). She's also correct that embryonic stem cells are harder to control than their adult counterparts. A recent study did, in fact, demonstrate a cure for Parkinson's disease in rats using embryonic stem cells; it also demonstrated that the "cured" rats subsequently developed fatal brain tumors. This problem may be solvable, but the author is correct to note that it is indicative of the extreme technical difficulties associated with embryonic stem cells.
More importantly, though, all of these technical details are really beside the point. The real issues here are all moral. A few years ago I read a fawning Discover article that bluntly described its subject as "a stem cell researcher who doesn't have time for your ethical hangups because he's working to save his children." The man's kids, you see, are Type I diabetics, and he's resolved to find a cure for what ails them no matter how many human embryos he's got to chop up. Unfortunately, the Discover piece failed to ask the critical question: if his research involved rounding up adults or small children and chopping them up against their will, would we excuse this behavior on the grounds that he was trying to save his children?
The answer to that question is painfully obvious; a scientist who made a habit of offing hobos to further his research would be imprisoned, and likely executed, no matter how valuable his results were. (Though I hate to run afoul of Godwin's Law, I'll note that there is precedent here in the fates of the Nazi concentration camp scientists, who were quite appropriately punished for their methods despite the medical value of their results.) Specifically, then, the relevant questions center on whether live human embryos are in fact live human persons, and whether or not they've got a fundamental right not to be killed pursuant to this status.
I don't have an answer to these questions for you. It's important to note that no other scientist has the answers, either; science simply does not address these issues. You have got to decide to what degree you think the live human embryos are equivalent to live human persons. You then have got to decide what rights you think this level of equivalence bestows upon the embryos, and what level of legal protection we should afford those rights. These are hard questions. But scientific judgements about the potential value of the results of embryonic stem cell research is wholly irrelevant to the answers.
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