Abortion/Contraception

I'm not really qualified to debate the statistics cited in the NY Times article.  They appear to be based on studies by the Guttmacher Institute, which several MOJ readers have e-mailed me to criticize.  I'm willing to take them with a grain of salt.  But I think the more interesting question is what, if true, these statistics suggest about the proper legal responses to the Church's moral teaching on abortion.  If it were the case that prohibition of abortion does not actually decrease the number of abortions but simply drives abortion underground (with resultant harm to women who choose to procure illegal  -- and often unsafe -- abortions), as appears to be the case in at least some countries, then does categorical moral opposition to abortion require support for its legal prohibition?