Micro,
It's a human embryo, all it can ever do is become a fully developed human (the gestation process) and then be a human until it dies from whatever cause at whatever time.
If it fails to implant, or miscarries, that is in the hands of fate/G-d/what-have-you, the hand of man has not intervened to take that life. That is an important distinction.
However, if another human takes active steps to deliberately end its life, that is one human life killing another (even if it is merely a potential human life, it's the human that counts).
Under almost every legal and ethical code worldwide there are rules governing when the taking of one human life by another is justified. However, in this case it is the laws and ethics of the US that matter.
A human life, that does not threaten another (which is the definition of "innocent" as far as US homicide statutes go), cannot be killed for reasons of convenience or the general welfare even of society as a whole. It can only be killed when it actively and directly threatens other particular, distinct individual human lives.
That's a valid legal position and argument as buttressed by statutes protecting only slightly more developed human life in the womb, which does not threaten the mother's actual physical well-being, from criminal or negligent homicide. Even abortion's legality is based strictly on the right of the mother, not on any benefit to society as a whole. The mother's right to abort, being based on privacy, cannot be rationally extended to any right for her or anyone else to benefit from that legally permissable killing.
Ethically the idea that human embryos, human life, might be deliberately, purposively created simply for the purpose of killing them in search of cures for other humans ills treads painfully close in spirit both to slavery (owning and treating other humans as tools to be used and discarded, not as people) and the euthanizing of other stages of human life deemed less worthy (due to their cost and lack of benefit to society and/or lesser "humanness" due to mental issues).
Ironically much like the very lives of some of the folks (physically and mentally disabled) and their families who desire gov't funding for this research to end their own uselessness to society and themselves.
We've seen that sort of assigning of value to human life in this country before and it is being proposed again in enlightened Europe, "for the good of society".
Without consistency on the worth of innocent human life, no matter how unlike ours, the urge to move the lines on what is permissible to do to that life becomes entertainable. The results are uniformly horrible.