But the broader topic of stem cell research involves up a number of difficult issues.
Any sort of decision generally requires an evaluation of alternatives. Stem cell research brings up several dimensions of values, that seem to sort themselves into a hierarchy. At the top of the value hierarchy are ethical questions, of right and wrong. Scientific research should not involve criminal activity. But in drafting legislation and regulation the question becomes, which sorts of activities should be marked off as being criminal? Perhaps where these lines have been poorly drawn, there may in fact be a moral imperative to engage in illegal activities - or at least a moral imperative to avoid some activities that are wrong despite being legally permissible.
At the bottom of the value hierarchy lie issues of cost. All other things being equal, it makes good sense to pursue any activity, including scientific research, in a cost-effective fashion.
The value of knowledge gained, of new scientific laws discovered, of cures finally established for diseases etc., the value of such scientific progress seems to fall at an intermediate level, between moral imperatives and cost considerations.
Values don't really arrange themselves into such a neat hierarchy, though, at least not in any way obvious enough to insure consensus. In general it is wrong to shorten people's lives with untested medical procedures - but for every procedure, someone has to take the risk of being the first test subject. In general it is wrong to raise animals just to kill them, but if there is enough economic value or reseach value gained, killing animals is considered acceptable by many people and by U.S. law.
The debate over whether stem cells constitute human beings or not is not an isolated question, but deeply entangled with the debate over abortion. That's another aspect of the interdependency involved in such issues. Whether or not stem cells are human beings or not is already a complex question when limited to matters of petri dishes and microscopes. But a decision one way or another will enhance the political power of the winning party, and provide a precedent for decisions on related issues.