Tell me something:

Suppose we still had slavery in this country.  Suppose you are anti-slavery.  Suppose further than you along with all the others against slavery were protesting to get the laws changed to outlaw slavery.  Suppose someone asked you whether you were willing or able to take in a freed man or women and care for them--and you said you were not.  Suppose they said "Then you can't claim to be anti-slavery--if you are not able or willing to take in freed slaves and care for them." Would that entail that slavery is morally justifiable? 

Here is my point: after birth is not the point.  The subject is abortion.  Whether I care or not what happens after birth does not effect the moral question of abortion.  Your logic basically says "Murder is morally justifiable because you only care that the child does not get murdered. You don't care what happens if the child lives."