and with more reason, i'd define humanity in terms of the mind; once the structures that support cognitive function start to develop, then the humanity of the child also develops. At that point, you want to close of abortions, as the fetus continues to develop into full personhood upon birth.
The counter I've seen JD parry with weakly before was that we do a similar favour for coma patients, as well as even more nebulously, patients induced into a chemical knockout, i.e. keep them alive based on their potential to (resume) attain cognitive function.
I'm not going to bother commenting on that one, other than to say, it's a stretch... a reach, on the same level as fox news pundits are going through now.