2 Chronicles 23:12-13. Athalia, hearing the noise of the people, goes into the house of the Lord and sees young Joash having been made king, to great rejoicing and fanfare. She rends her clothes and cries "Treason, treason."

Athalia was a very wicked woman. When her son, the King Ahazaiah, was killed by Jehu, Athalia then killed the entire family of the house of Judah lest they take power, and was ruling in her son's stead. But the child Joash was saved from the slaughter and kept in hiding until upright leaders and priests concocted a plan to crown him the rightful king.

All of that being said, however, I bet that Athaliah truly did believe this was treason. She was the mother of the dead king, and probably believed she was the rightful ruler, and that crowning a new king behind her back was treason. Maybe it even was, technically, treason. 

Athaliah was wicked and power hungry, and those traits corrupted her mind. That is what sin can do to us. We can become so warped to the true and the good and the beautiful, that we see evil as good and good as evil. Further, the devil is incredibly legalistic, and once he's got us sinning, he will always try to find a way to convince us that we are, in fact, in the right, even when we have been doing outrageously bad things.

I think if we have to hang our hats on legalistic terms and definitions, or on data sets and statistics that do not reflect reality, to try to justify ourselves or impose our will on others, then we can be pretty sure that we are not in the right. We need to step back from the situation, especially when our passions are aroused, and look at reality. Did we really do everything right in getting to this place? Have we been virtuous? Are we truly evaluating the situation from a point of view of trying to find the truth and preserve the good? Often, if we are honest with ourselves, the answer is no.