Problem #1: He is drawing a direct parallel between Islamic (Sharia) law and having a Christian version thereof. In other words, he is saying we should do what they are doing while at the same time, many conservatives are railing against Sharia's (non-existent) threat to the U.S. Unfortunately, the GOP is too addicted to hypocrisy to see this.
Problem #2: This would mean that, by law, you would have to love thy neighbor as thyself, which is something Santorum has never been too keen on. Just look at his record and how he has treated/represented his gay constituents in Pennsylvania. He plans on extrapolating that to the rest of America at such time as he becomes President (which is quite likely never).
Problem #3: Him believing that abortion is categorically wrong, even for health reasons, doesn't jive with the fact that his wife had an abortion. Granted that her life was at stake and most people (myself included) would not be against her having the procedure, most people in this case excludes her own husband. According to his own statements (at least if he had the courage of his so-called convictions) would have her tried for "Murder for Hire." Here again, the political right is addicted to hypocrisy.
Problem #4: This won't help his poll numbers, so it will only matter but so much.