Mishnah Kiddushin on the Laws of Witnesses to the Process of Kiddushin

The Mishnah tractate Kiddushin describes the process by which a woman is legally married by her husband. Generally in Talmudic law, witnesses are required to be present in order for an act to be considered legally binding. However, consider the conflict instigated by the very first mishnah:

"A woman many be acquired in one of three ways: through money, through a document of betrothal, or through cohabitation." -- Mishnah, Kiddushin 1:1

The commentators indicate their sensitivity to the laws of testimony:

THROUGH MONEY : "He gives money or an object of monetary value. This must be performed in the presence of two witnesses." -- Rashi

THROUGH A DOCUMENT : "Her gives a document which states that she is betrothed to him." -- Rashi. "It must be handed to the woman in the presence of two witnesses." -- Rambam

THROUGH COHABITATION : "He cohabits with her, telling her in advance that he is betrothing her through intimate relations." -- Rashi. "The witnesses do not observe the actual act, but observe the couple entering a private place together." -- Rambam

I find Rambam's last comment here to be interesting, since it conveys an ethical value that is not readily apparent in the original text of the mishnah.