Alice does something controversial for a particular reason. Her actions have bad and controversial consequences, but also have an outcome that she did not intend, which nearly everyone finds extremely desirable. Bob argues Alice's actions were justifiable because of that unintended but desirable outcome.
Is there a commonly-accepted name for this sort of argument?
Edit: I think this might be known as the Historian's Fallacy. http://en.wikipedia.org/wiki/Historian%27s_fallacy