ABC News' Emily Friedman (@EmilyABC) reports: In an oped today on the National Review's website, presidential contender Mitt Romney outlined his position on abortion and explained why, unlike five of the other Republican contenders, he did not sign the Susan B. Anthony's List Pro-Life Presidential Pledge. "As much as I share the goals of the Susan B. Anthony List, its well-meaning pledge is overly broad and would have unintended consequences. That is why I could not sign it," wrote Romney. "It is one thing to end federal funding for an organization like Planned Parenthood; it is entirely another to end all federal funding for thousands of hospitals across America. That is precisely what the pledge would demand and require of a president who signed it." Fellow presidential hopeful Herman Cain also declined to sign the pledge while, according to the Susan B. Anthony List, Michele Bachmann, Newt Gingrich, Ron Paul, Tim Pawlenty and Rick Santorum all agreed to sign the list. Romney wrote that another reason he declined to sign the pledge was because he believed it "unduly burdens a president’s ability to appoint the most qualified individuals to a broad array of key positions in the federal government. "I would expect every one of my appointees to carry out my policies on abortion and every other issue, irrespective of their personal views," he wrote. Romney last spoke about his stance on abortion rights at the CNN debate in Manchester, N.H., last week, when he said that he would "support justices who believe in following the Constitution and not legislating from the bench." "I believe in the sanctity of life from the very beginning until the very end," he said. But this isn't always how Romney has felt. In 1994, when Romney was running for U.S. Senate against Ted Kennedy, he said, "I believe abortion should be safe and legal in this country." Then, in 2002, during his bid for the Massachusetts governorship, Romney vowed to "preserve and protect a woman's right to choose." During the debate last week, Santorum was asked by host John King if there was any reason to doubt Romney's position on abortion rights, considering that the former Massachusetts governor was at one time pro-choice. Santorum responded that he thinks the "issue should be, in looking at any candidate, is looking at the authenticity of that candidate and look at their record over time and what they fought for." But today, Santorum had harsher words for Romney, saying in a press release, "It is incredibly disappointing that Governor Romney chose not to defend those who cannot defend themselves."