Just as there are a relatively few of us on this side of the debate, there are also relatively few who hold hard positions on the other side of the debate.
The only debate available is for the moral attention of those who do not have a strong position for or against the use of ESCs (they haven't really done much thinking about it), but who are strongly attracted by the pragmatic applications of the research.
In that sense, this issue is no different from the abortion debate. When asked to decide whether specific abortion procedures should be allowed, most people say "no." It's only when they are asked to decide on an undefined "right to choose" that a majority of people think abortion is OK.
What that tells me is that people are capable of doing the moral calculus if forced to do so, but aren't really willing to do it on their own. What has to change -- in the case of abortion, and in the case of ESC research -- is the tendency for people to avoid the moral questions.
When you reduce it to a matter of pragmatic "it will work" or "it won't work" arguments, our position collapses. All they have to do is wave the "life-saving treatment" flag, and we're left trying to say "but it won't work." We always lose those arguments.
When there are many arguments in favor of one's position, I don't think one should eschew the pragmatic arguments merely because principled ones also exist. Indeed, I think one should put forth the pragmatic arguments as a means of exposing the fact that much of the support for ESC research is driven by a pro-abortion agenda rather than any bona fide desire to [non-fatally] treat diseases.
I suspect that it would probably be possible to produce a motor vehicle fuel from pine sawdust. If I spent enough money on such a project, I could probably succeed at such a venture. That does not mean that such an expenditure would be wise. Other uses of the money would make far more sense.
I have seen nothing to suggest that ESC research would have any more promise than ASC research, given the same level of funding. Even if the embryos destroyed in such research were considered to have no value beyond their production cost, I still see nothing to suggest that ESC research is an economically-sensible means for developing the types of treatments researchers are claiming to seek.
Of course, if the researchers really have other goals, ESC research may make a lot of sense...