Bill Bennett tells the National Review that Gov. Sanford should resign. He gives a quote from Chuck Colson on integrity to explain why:

Integrity means every part of your body. It does not mean every part of your life. It means every single part of your existence. All those water tight doors are shut tight. And then there is integrity. You cannot say that someone can do something on the private side of their lives without it having public consequences, because you’ve opened one of those watertight doors and that ship will eventually sink. A cheat in private is going to be a cheat in public. Someone who lies in private is going to lie in public, and you can’t trust someone who does that.