Are you a pacifist? If not, then do you view the droppings of the atom bomb on Japan as a way to actually save lives that would have normally been lost in standard warfare?
I have a hard time seeing how embryonic stem cell research is the same as warfare.
If you support the above, then you must also support ESC research because that is a way to potentially save lives that would be lost. Potentially living persons (as defined biologically) will be terminated, but they will feel no pain and they have not developed enough to have thoughts. People that do feel pain and have real lives will be saved from pre-mature death.
Again, they're not the same.
Embryonic Stem Cell research uses cells from fertilized human eggs. Those blobs of tissue are considered human or persons by many of us. Per the 5th Amendment, no person shall be deprived of life, liberty or property without due process of law. Abortion does just that.
The decision to drop the bomb on Hiroshima and then, Nagasaki was made by a president who was given the authority to conduct war. Congress declared war on Japan on December 8, 1948. In this case, the decision to drop the bomb was made through due process.
The promises of Embryonic Stem Cell Research remain mostly unfulfilled. There is a possibility that it may produce results, but there are also great difficulties to be overcome (rejection by the host body, difficulties in getting the cells to specialize into the desired cell type etc). On the other hand, adult stem cell research has already produced results. I think that I'd put my money on the horse that won some races rather than a pie-in-the-sky contender that makes big promises but has produced few, if any, results.
Oh yes, and if you're going preface your arguments with the words "scientists claim"... I think you should know that most of those scientists work for companies that stand to profit from embryonic stem cell research, so they may not be unbiased. I think I can find scientists who argue exactly the opposite position.
I've said this before, but I believe that it bears repeating. I believe that many people "out there" (and not anyone on this board) are pushing embryonic stem cell research not out of an interest of saving lives but primarily to justify abortion. I really don't think that society should be in a position where it manufactures human embryos just to harvest parts. I wonder how people who support ESC research would feel about harvesting organs from executed criminals in order to save lives? It seems pretty barbaric to me and reminds me too much of the premise made by the movie "Soylent Green". In that movie, in a future world the dead were turned into food for the living.