From what I've read (and thank you, MHGinTN, for your wonderful essays and comments about all these related topics!), embryonic stem cells haven't been "useful" anyway. Apparently (someone correct me if I'm wrong) some kind of cells from bone marrow? Or at least from adults, taken harmlessly, show more promise medically.
Two points may shed a small amount of light on this.
1. Those who abhor moral absolutes are by definition placing themselves and others like them on the pinnacle of authority, due to envy of God. Therefore, they reject out of spite and hatred His laws, both the laws of nature - life and death - and moral laws, such as equating same sex acts with the conjugal relationship between a husband and wife. Such rebellious souls, since they cannot create life (only God can) want to destroy His creation. You can see how they are attracted to death: abortion, euthanasia, the "right to die", Peter Singer's statement that infanticide has its virtues, and last but not least, sodomy.
2. A corollary is their fanatic attachment to the artificial or unnatural life of the body. Even if embryonic cannibalism COULD extend or improve my physical being, I would reject it with not a second's hesitation, because I know without doubt that life is not physically based. I am not a body with a soul, I am a soul waering a body. Death means I, the eternal soul, leave the body. I am therefore not afraid of death. Death is not a tragedy. Living a life of rebellion against the laws of Nature and Nature's God is a tragedy.