But a beating heart doesn't a person make (otherwise horses would be human too.)
To be intellectually honest, you should note that this is part of an effort within medical history decide upon a logical end to life. Not a logical beginning.
The difference is significant.
When a formerly functioning brain stops functioning, it is terribly unlikely to ever begin again, regardless of medical intervention. Hence it is a reasonable standard after which to assign medical death.
When an early gestational brain is not yet functioning, it is VERY likely to begin functioning in the near future. Hence this would be an unreasonable standard upon which to assign "sub-humanness" or some other similarly nonsensical designation.
Human beings have medically known stages of development. Provided a human is functioning as it should considering its stage of development there is no medical reason it should be considered as anything other than a living human.
Those who wish to delve into more mystical realms to devise an excuse for killing the unborn will doubtless be undisuaded. Nevertheless, once one resolves upon a right to human life, the unborn fetus has excellent ground upon which to stand.