If you oppose abortion because you are killing potential life, not because you are killing life, then you would, if being rational, also oppose contraception because it is preventing potential life.
I realise people wouldn't necessarily equate the two, but if the problem is "potential life" and not "life", then contraception stops the potential life just like abortion -- unless of course you see a different between potential life and the fetus, in which case we are back to the fetus being something more than simply "potential life".
What is so important about "potential life" that we would ever want to discourage a 14-year-old from fulfilling that "potential life" if she got pregnant? I realise you are trying to make a distinction between "potential" and "actual" life, but I contend that potential life isn't a rational reason to oppose abortion in many instances.