Sex between biographer and subject -- was that wrong?

Instapundit points to this item from Walter Russell Mead in which he condescendingly explains that a biographer shouldn't have sex with the subject of the biography if the subject is married to someone else.

Sorry, those tired old ethics were repealed during the second Clinton term when we learned that sex, lies and stained dresses were business as usual for busy executives.

It brings mind George Castanza's confusion when accused of having sex with the office cleaning lady. Was that wrong?

As for Paula Broadwell and General David Petraeus, don't-ask-don't-tell was the mantra of the day, but they mistakenly thought it applied to them. Like Castanza's situation, maybe no one told them otherwise.