> You can't "just regulate the smiths" like some 21st century despot because those smiths also make the iron tools those people need to farm to pay your taxes.

There is a superstition in the Middle Ages that blacksmiths should not be killed, in the context of battles. Blacksmiths were an absolutely essential part of the support of an army, but his skills and tools were just as useful to the winning side. Minus his skills, his tools were just surplus, heavy items.

Other army support crew like washerwomen, stable boys, and even prostitutes were of course much easier to replace.