Well, my view of Original Sin might be different from Lutherans but I do not see how being totally depraved influence abortion, a lot of people would be considered totally depraved but we still care about them.
What he's saying is that if we take the verse to mean that David possessed an inherited sinful nature from conception that it would therefore not be a stretch to suggest that David was a morally valuable, created in the image of God, soul possessing human being from conception.
And if that is the case, then surely at the very least the 98.5% of abortions committed for convenience reasons would be immoral.
It all starts to add up.
1. From Scripture we know that all human beings are created in the image of God and possess inherent moral worth and value.
2. Scientifically we know that a new human being, with its own identity, and unique DNA comes into existence and begins a 25 year developmental period at fertilization.
3. There are 0 Scriptural examples of a living human being without a soul.
4. John the Baptist was both filled with the Holy Spirit and leaped for joy
while still in his mother's womb.
5. David indicates that he possessed an inherited sinful nature from conception.
6. While Scripture doesn't directly address abortion in a clearly outlined statement, it is clear that the ECFs acknowledged it was wrong. The Didache addresses it directly.
For me, I haven't seen any good reason to think that the unborn are any less human or any less morally valuable than the born. I don't see Scripture discriminating again a human based upon their age, developmental level, or location; so I don't see why I should.