Full Idea
It is hard to see how the 'potential' argument can succeed against abortion without also succeeding against contraception.
Gist of Idea
If abortion is wrong because of the 'potential' person, that makes contraception wrong too
Source
Jonathan Glover (Causing Death and Saving Lives [1977], §9.2)
Book Reference
Glover,Jonathan: 'Causing Death and Saving Lives' [Penguin 1982], p.122
A Reaction
It would even make it wrong not to introduce a given man to a given woman, if you thought they might be attracted! Maybe 'incipient' would be a better word than 'potential'? A person has been 'initiated'? Do words matter that much?