|Medieval Occupations [source]|
One taboo was about blood. Spilled blood was not a good thing, and so those who dealt with blood were to be kept separate from the rest of the community: executioners and soldiers, of course, but also butchers and surgeons.
Another taboo involved filth and impurity. Dyers and fullers of cloth and textile workers had hands and skin stained by the chemicals used in their trades, and were considered unclean. Those who washed dishes and laundry also dealt with much dirt (even though the object was to make things clean), and were not high on the social ladder.
Money was a taboo, especially thanks to Biblical lessons about a rich man and the eye of a needle (Matthew 19:23-26 and other Gospels), Jesus upsetting the tables of the moneychangers in the temple (Mark 11:15-19 and other Gospels), and the injunction against usury (Luke 19:22-23 and other Gospels).
Innkeepers and bath keepers ran places that could be the site of improper behavior. Tavernkeepers sold wine. Cooks were the purveyors of gluttony. Although not outlawed, all these professions were considered with suspicion.
One wonders how the middle class ever grew!
*University of Chicago Press 1980.