Richard Swinburne and abortion

Here's an interesting passage about when "we" begin from the famous Christian philosopher Richard Swinburne:

Interesting, despite what he says here, Swinburne argues that abortion is wrong basically because although there is no person "in" an early fetus--nobody is there, so to speak--that body is necessary for there to be a person and it's on its way to a person inhabiting it, and so it's wrong to kill that body. 

Now, is that a good argument?