The slippery slope argument can be a logical fallacy. "A" might often lead to "B" but not inevitably to "Z".
But the argument sometimes plays out. Witness the January/February issue of Neurology Now, in an article on "The State of Stem Cell Research".
It was written before President Obama reversed the ban on Federal funding for embryonic stem cell research. It begins,
Will the brain benefit if President Obama reverses the Bush administration's restrictions on embryonic stem cell research?
The writer, Tom Valeo, makes efforts to be fair, recognizing that there are viable research paths that do not use embryonic stem cells:
...the Bush ban has had one positive side effect: researchers have begun investigating the therapeutic potential of other types of human cells.
Then, in comments by Lorraine Iacovitti, Ph.D. of Thomas Jefferson University Medical College, we slip into a reasonable sounding argument - a short period of research on embryonic stem cells will make future use of embryonic cells unnecessary:
"I believe the embryonic stem cell lines are the gold standard because they're the only stem cells that reliably become dopamine neurons after they're transplanted into the brain," says Dr. Iacovitti. "But the ultimate goal is to make adult-derived tissue behave like embryonic stem cells. That will be the wave of the future because it will allow patients to provide their own replacement tissue."
Then, toward the end of the article, we get this horrific bit of news without fanfare:
Ping Wu, M.D., Ph.D., of the University of Texas Medical Branch in Galveston, is working on a way to use neural stem cells taken from human fetuses to replace damaged spinal cord motor neurons, thereby enabling paralyzed people to walk again.
"The brain needs help."
"There are viable ways to do this without taking embryonic stem cells."
"But if we just take a few embryonic stem cells, we might not have to in the future..."
"Hey, let's see what we can do with fetal cells."
Oh, and there's a box in the article that explains what stem cells are. Embryonic cells come from "a hollow ball of 50-100 cells known as a blastocyst." Sounds inert, not human. The box conveniently neglects to define the host from which fetal cells are taken.
Here's what Merriam-Webster has to say:
Middle English, from Latin, act of bearing young, offspring; akin to Latin fetus newly delivered, fruitful — more at feminine
Date: 14th century
: an unborn or unhatched vertebrate especially after attaining the basic structural plan of its kind ; specifically : a developing human from usually two months after conception to birth
UPDATE: reader Steve L. from Canada sends along more evidence of alternatives to embryonic stem cell research.