Helen,
I think that the issue is the level of dispassion, like your example of St. Ambrose.
Because we know what is taught by tradition and we can see what is around us, but dispassion should be exercised in our hearts. So there are two views..one of dispassion and one of passion(due to weakness of the mind). One person who is blessed with dispassion can say: There is a woman who doesn't cover her head and the other person with passsion can say: there is a woman that doesn't cover her head.
Both, make the same observation, but one has peace in the heart and the other is disturbed. The same sentence, but from a different source.
We know what is right to do, in the eyes of God, but the way we view others becomes our sin, if we allow it. The saints are the perfect example of dispassion.
It's important to see what is happening around us and take a stance for truth, but if we do it with anger, then we are defeating the whole purpose.
We lose sight of the true enemy and instead target the instrument. There will only be another instrument to follow afterwards, but we never get to the source because we are always fighting these senseless battles with the instruments.
They're like decoys.