I agree with this completely. And it's not just choice ... it's also guns. What would the NRA do?
Even beyond volunteers, the communications channels of the GOP anti-choice and gun organizations are huge. If you've never known a plugged-in social conservative, you have no idea how much information they get through that channel (email, church bulletins, conversations at church, sermons); I'd say it's their primary news source by far. And if they aren't working for the GOP nominee, I don't see how he stands a chance. Same thing with the NRA communications channels.
Basically, if the nominee is anyone other than Hillary, Giuliani gets crushed in an historic manner. Richardson may not be my first choice, but if by some strange twist of fate it's Giuliani-Richardson, the GOP would be in enormous trouble.