It's not a child. Even if you want to use a broad definition of child (and I do), this cell was not implanted in a women, and could not grow.
It's one thing to take positive action to stop a child from living (abortion).
It's quite another to simply do nothing. This type of stem cell research is done from cells that would otherwise be thrown out - you have not prevented a child from living.
It's really not what? Not a positive action that kills a child?
You have to see a difference between not saving someones life, even though you can, and actually going and killing them.
> You can’t make someone host a baby they don’t want
We are getting offtopic here, but sure you can. We make people take care of their children all the time. If they don't they go to jail for neglect or abuse.
Sure, we know that humans expect small pieces of human to be treated as irrelevant (e.g. you leave tiny skin particles and hairs basically everywhere and all you usually ask is that people vacuum them up to avoid the place being covered in dust) and that larger pieces (e.g. a toe, or in this case an embryo) should be treated with extra care and consideration of people's emotional reaction.
But it's not kidnapping if you keep someone's toenail clippings. It's creepy, but it's not kidnapping. It's not murder when the barber sweeps all the hair into a furnace, it's called tidying up.
Do you genuinely believed that a baby was killed to harvest stem cells? If the baby was already dead, are you morally opposed to using an unsaveable baby's stem cells?