It would appear that Romney doesn't want to be held accountable.
Romney Rejects Pro-life "Pledge" as Flawed
Former Massachusetts Gov. and current GOP presidential frontrunner Mitt Romney is refusing to sign a pledge penned by the pro-life group 'The Susan B. Anthony List.' The pledge calls for the nomination of judges "who are committed to restraint and applying the original meaning of the Constitution, not legislating from the bench."
It also demands the selection of pro-life appointees for cabinet positions and the advancement of "pro-life legislation to permanently end all taxpayer funding of abortion," as well as the defunding of Planned Parenthood.