If you're a pro-choice Republican running for president, by all means go ahead and try to downplay your pro-choice views in order to emphasize what unites Republicans. Feel free to try to make the case that pro-life Republicans should bracket that issue. You won't convince everyone, but I have no problem if you make the case.
But please don't try to use disingenuous rhetoric masked as an argument when you try to make your case. It's simply deceitful to pretend your opposition to laws against abortion is emphasizing "what we are for" rather than "what we are against" and that others' promotion of the inherent worth of the unborn is "what we are against" rather than "what we are for". Virtually any policy you approve of can be characterized in terms of being for something or against something, and Rudy Giuliani himself regularly characterizes his view on abortion as being against putting people in jail for having abortions, which is a disingenuous mischaracterization of the pro-life view to begin with, but even aside from that it's very much being against something.
Thanks to Nancy French for noticing this.