Since these tax rules only work on unwinding a legal marriage and not on any form of cohabitation, they remain a gross tax inequity the gay marriage debate has never thoroughly addressed.
And if the person doesn't resist that impulse, you have to have some form of legal authority to make sure that they're not infectious during their travel back to the United States.
Turning from ancient history to more recent events, Lord Forsyth's point was that the FM had form: that he could not be trusted, as witness the episode of legal advice with regard to EU membership.
If you like (and this is not strictly accurate in a legal sense but is good enough) there needs to be a marriage of form and function for there to be passing off.