I think everyone who is pro-life can agree that we don't want to see even one more abortion take place. Which approach do you think is better -- a person who is rigid, and is going for the whole enchilada versus the other person whose end goal is the same but is willing to accept a compromise to get 1/2 of the enchilada and is able to prevent a great number of unborn babies from being aborted while the other is largely unsuccessful in preventing abortions because of his/her rigidity? Wanting to end abortions immediately is a noble cause but not realistic. How many people do you think could be persuaded to support a law which outlawed all abortions without any exceptions in cases of rape, incest, or the danger to the life of the mother? Then, think again... how many people do you think would support a ban on abortion with allowing for exceptions in cases of rape, incest, or danger to the life of the mother? I think there would be a substantial difference between the two.
Dr. Gerard M. Nadal makes a good case for the incremental approach. You can see his arguments here.