I'm not a math guy but I'm pretty sure that's not how probability works. Also, it doesn't factor in your ages (fertility) or miscarriage.
Regardless, then I hope you also won't approve of abortion if you're not willing to maximize your preventative measures. Most people don't which is exactly why we're having this debate.
I think that'd be redundant in light of the fact that proper, maximal contraceptive usage has a very low failure rate (again, on top of the fact you're far from guaranteed to become pregnant even without contraceptives).
Even if they did use some form of contraceptive, people don't always use them properly, or elect not to maximize their efforts in avoiding pregnancy. That's like slapping your seatbelt on halfway or not at all; and if you don't use it properly and install an airbag, then it's your fault if someone has to clean you off the road.
I'm not telling you to walk, just drive safely instead of retardedly.