Earlier quoted context omitted.
Okay, on day 19 three of them are clusters of cells, how about day 280? How about year 5? I think the argument is that a majority of people would find it unethical to continue to develop viable embryos, and even more unethical to conduct research on them were they to mature.
Research is already performed using human fetal tissue obtained from aborted fetuses. How is this significantly different? "A majority of people would find it unethical to continue to develop viable embryos" seems contradictory to the current legal status of abortion in the US. Perhaps it is unethical but worth doing regardless?
They are a compromise to help women who made a mistake, were victims of assault, are too young to take care of a child. It's a bit less about "taking ownership of your body", than it is about "being tolerant and understanding about facts of life we can't change".
That's where it's less unethical: it's not like people support terminating a potential human life, they support instead lifting one up that took a wrong step.
Now these chimera experiments are fine to me, but I'd be okay to wait, go slow, debate in society about them rather than point at 16 yo rape victims and say "see she killed her baby and we used it to test a vaccine, why can't I mix a monkey with a human and see what grows before terminating it when I dont need it anymore"? Again, I m anti religious but I wouldnt want street riots and Trump 2.0 because scientists felt it was boring to explain to the idiots.