To provide some historical input:
"Medieval attitudes towards violence were based on a simple principle: decent people may fight, but they don't steal. Theft was dishonorable and, consequently, violence performed to enrich oneself at the expense of a fellow person was dishonourable too. (...) At the local level, whenever a man used violence to appropriate his neighbor's goods, he ceased to be a respectable member of the community. Furthermore, to attack someone secretly, from behind or in the night, was disdainful, because it's motive, if not robbery, was akin to that of robbers. Hence the medieval legal distinction between murder and manslaughter, which defined the first not primarily by the criterion of premeditation, but by that of sneakiness. A case could be prosecuted as murder and lead to execution when the act had been particularly heinous, because it had been commited at night, without a warning, because the body had been hidden afterwards, or simply because the victim was a pregnant woman. (...) Murder, in the legal sense, was infamous, whereas open and public fighting, even when casually ensued, was honorific."
After Spierenburg P., A history of Murder: Personal Violence in Europe from the Middle Ages to the Present
I think we can clearly conclude that Infiltrators as portrayed in BM are not only dishonorable (at least in the parts of Europe covered by the book: Flanders, Northern Italy, France, England and Germany), but also unrealistic - according to this source.
