Political opponents reacted by calling Obama "behind the times" on stem cells. After all, there are now ways of making ES cells without destroying embryos:
If you listen closely to Obama, you'll realize that he knows this, too. But he also realizes that Bush's opposition to ES cell research was a symbolic gesture - fueled by anti-abortion ideology, not science. By overturning the Bush ban, Obama is laying down his own criterion for science policy - that it should be guided by facts, and not ideology.
What are the facts? The embryos used to derive embryonic stem cells are tiny balls of about 100 cells, without sensory organs or circulatory systems. Our society is willing to discard them for the sake of IVF, just to give parents their own biological child instead of adopting. Certainly, we should be willing to discard them for the sake of research which may cure untreatable diseases. The destruction of adult farm animals, just so we can enjoy the pleasure of eating their meat, poses a far greater ethical dilemma than embryonic stem cell research.