dontconvert2islam wont break an oath; but can one ever be justified in doing so?

In answer to the video "Muhammad’s Christian Female Slave"

As already pointed, previously to the incident in the opening verses of Sura Tahrim, God sanctionned the expiation of oaths when it is something lawful. 

Nothing can be forcefully forbidden when God made a thing lawful 5:87, even if such an attitude happens to be motivated by the desire to please someone else, as in the prophet's case who sought to please his wives. Sometimes a human being under the influence of emotions without full consciousness of the seriousness of the undertaking, makes an oath and forbids to himself something permissible as was the case with the prophet, and in such cases the oath should be broken 2:225 and then atoned for 5:87-89. The first part of the verse

"why do you forbid (yourself) that which Allah has made lawful for you"

has a compassionate tone, because the prophet did it out of compassion. This however does not mean that he was justified in making something that is otherwise lawful, as forbidden. That authority has never been delegated to the Prophet, not to speak of any other man. The second part of the verse

"you seek to please your wives"

indirectly warns those who benefit from such act, not to knowingly take advantage of that situation. The position of a Prophet, and by extension that of any respected leader, is very delicate. Such eminent individual does not solely belong to himself but to a nation transcending time and space. The higher the person, the smallest sins are enlarged as if they were enormous. A minor incident experienced by an ordinary man in his life may not be of any consequence, but it assumes the status of law when experienced by a Prophet with a large a devout following looking up to him as the epitome of good manners and spirituality. The life of such a person must remain in line with the divine will, and openly explained to present the right example to follow

62:2"He it is who has sent unto the unlettered people an apostle from among themselves, to convey unto them His messages, and to cause them to grow in purity, and to impart unto them the divine writ as well as wisdom - whereas before that they were indeed, most obviously, lost in error".

Similarly, the prophet's pious wives too are to become an example for all women of the ummah, more than any other woman, they should be mindful of God's limits. The Quran often alludes to these notions in regards to the prophet, his wives and the leaders of a community in general, hence God's will to

33:33"remove from you all that might be loathsome, O you members of thehousehold, and to purify you to utmost purity".

Had the fine details of the prophet's oath and of the betrayal inside his household 66:1-3 been of any importance to the general message of the verses, then the Quran would have mentionned them but disclosing them was entirely irrelevant to the point and could even distract the audience's attention from it. The secret shared by the prophet and then disclosed by the wives, has thus been altogether ignored. What has been disapproved and pointed out in particular is the very fact that the secret was disclosed to another. The point of the passage is that the violation of the spouse's secrets violates the sacred law. And this applies whether to the husband or the wife. This is subtely alluded to at the end of the sura, where Mary the mother of Jesus is mentionned alongside Pharao's wife as the example to follow. The word describing her submissiveness is in the masculin plural/qanitin 66:12. This necessarily includes the male gender as well as females, otherwise it would have said qanitat.

This eloquent, linguistic precision makes her not only a role model to Muslim women in her chastity and submission, ie submission to the divine will, but also to Muslim men. 

It is interesting to note the tact of the prophet in such tense situation. When the disloyalty towards him from within his household was uncovered, he informed the guilty wife of SOME of what she had revealed, just enough so as to make his point, but refrained from informing her of it all to prevent her further abasement and shame

"he made known part of it and avoided part".

As reported in the traditions, this particular attitude was noted by some of the early followers, including Ali, and acted upon. It is to be noted that the Quran in several instances unveils to the prophet the secret behavior of his contemporaries, especially so among his enemies 2:14,76,3:119.