"Since when does a marriage license make it less easy for a man, or a woman for that matter, to pick up and leave at an inconvenient time?"
Uh...are you stuck on stupid, or what?
"I know just as many unmarried "domestic living" couples in stable relationships as married couples in stable relationships."
No, you don't.
Either that, or you know the wrong people.
Fine, don't answer the question. You think just because people are in a "legitimate" relationship, they will be less likely to leave than those in an illegitmate (ie unmarried) relationship?