Because there are limits as to what adult stem cells can do, while there is no limit for those recovered from blastocytes. This approach goes for limited instant gratification at the sacrifice of the long-term goal of even greater good. We need to invest in both.
I find it interesing all these "scientific" attacks on pluripotent stem cell research. Researchers are going on Capitol Hill and in the media to talk trash about pluripotent research. I've finally figured out the motivation -- there are a limited number of grant dollars, and unethically trashing the competition that means more for them.
The relevant question is not whether fetuses are human lives, but whether killing innocent human life is acceptable or not.
Those who think it is acceptable are called psychopaths.
You do not know that embryonic stem cells are without limit, any more than we know that adult stem cells are limited. That is all hype, unproven. We have not been able to induce any embryonic stem cells to differentiate into the 3 different cell groups, but we have been able to induce multipotent adult cells to do so.
http://www.insightmag.com/news/2004/05/16/National/The-Stem.Cell.CoverUp-682587.shtml
The unethical act is the killing of innocent humans. But, you're probably right about the money incentive.