Bingo!!
The essent�ial question is
Why do some embryonic stem cell researchers want to tinker with human embryos specifically?
The answer is: Because they know that human embryos grow to be bigger humans, rather than bigger cats or dogs or cows .
Human embryos are not merely potentially human.
Human embryos are essentially human.
If someone traded non-human embryos for human embryos in an ESCR lab, the researchers would become very agitated. !!
If the non-human embryos were equivalent to the human embryos, the researchers would not care.
As you so aptly pointed out...human embryos are different than other embryos.
They are a treasure that should not be destroyed.