Anti-abortionists aren't going to vote Democrat, nor are they going to vote third party, for reasons I have already told you.
Rabid anti-abortionists make up a small segment of the voting public. Even if 60% of Republicans are rabid anti-abortionists, that is still only 30% of the voting electorate.
Remember, Alan Keyes only got 27% of the vote running on anti-abortion and morality issues in a state where a very unpopular Bush got 45%.