firstly, embreyonic stem cells are not produced from aborted fetuses. Only cells 24-48 hours old are suitable... eggs and sperm are mixed in a petry dish, and 24 hours later disassembled under a microscope as they are too small to see with the naked eye (converstly, a woman doesn't know she is pregnant until at least a week since fetalization, and abortion isn't used until there is at least something visible to abort)...
When an egg and sperm unite, a human in his embryonic stage of life is the result...you and I and every human person were once in that stage of life....our very distinctive DNA was there. These cells are obtained by killing fellow members of the human species at a very young age.
Which says nothing about my point, there are not aborted fetuses used, they were never inside a woman, it is a zygote created in a lab and taken apart before it can form a fetus. However, from a biologists perspective I would say that this is the point of origin, that is, a person begins existing then... It is just a very fragile point of origin with massive death counts, there are the sperm and egg cells that die in the billions, but then when you do have a fertalized egg, it often fails and dies without the parent even noticing a potential pregnancy. and there are no souls, for anyone (again from a biological standpoint); but it is certainly the moment life begins for a person.
Let me put it this way, if you mix human and ape sperm/eggs then you also get a zygote, it dies shortly afterwards because it is too unstable to survive due to incompatible DNA, but a zygote forms (a few species that are really close to us have a zygote that can live for a few weeks). Does that mean that every instance of beastiality results in a living half human with a soul? Actually from a religious standpoint it makes more sense that God would only place a soul in a baby that is going to be carried to term. Much less not place a soul into a lab zygote (or individual sperm and egg cells)
In regards to their usefulness though, embryonic stem cells are actually easier to produce then adult stem cells, because you just need to take apart a zygote, and we do not yet fully know how to transform an adult cell back into a stem cell. This means that for the moment, ESC are more suited for research and for medicinal use. (despite having to use immune supressors with them)
It is just that in the future it is better to use ASC instead to eliminate the need and dangers of rejection, and the dangers of the immune suppressors taken to reduce rejection rates (causing other risks and complications.
Regardless, the moral issue is one I was not trying to address, but pointing out it has nothing to do with abortion.