Wow. This theory is still being expounded? Way wrong…
Medieval cooks didn’t use spices because they were covering up the taste of rancid or rotten meat. There is a very simple reason for this: eating bad meat will make you very very sick, and quite possibly kill you (especially if you live in a time when you can’t get electrolyte drinks or IV fluid replacement). Covering it up with cinnamon and pepper will not fix that. Medieval people did not eat rotten meat, because, while they didn’t have our modern germ theory, they were capable of noticing that people who ate meat that smelled bad got very sick and often died.
It is true that a lot of meat in the middle ages was not eaten right away, but then, a lot of modern meat is not eaten right away – what do you think aged steak is? And yes, accordingly, some of the meat eaten at the time probably had a somewhat different taste and texture than our refrigerated meats. (Also, not surprisingly, they very often dealt with the no-refrigeration problem by preserving meats, by salting or drying or sugaring or pickling or submerging in fat. But they preserved them before they went bad, because that’s the point of preserving.) And yes, absolutely, people in the middle ages liked their food heavily spiced, and also sweeter than most modern people do. But they liked it that way because that was what they liked; it was a luxury, and also just a preference. I like the way pickles taste, but that doesn’t mean I eat them because I had to do something with a bagful of rotten cucumbers.
But they didn’t eat rotten meat, because eating rotten meat isn’t something people do – our digestive tracks can’t handle it. It’s almost impossible to hide the smell or taste of rotten meat (being as it’s one of the things our bodies are designed to teach us not to eat), and even if you could, you’d get out of that habit pretty quickly after the first round of people got sick and died.
(Also, since spices were extraordinarily expensive, and therefore province of the wealthy, it just doesn’t make sense. You save nothing by refusing to throw out a piece of meat and instead putting on spices that cost many times the cost of the meat; it would be financially wiser to just throw out the meat and slaughter another animal.)
Medieval people didn’t think like modern people, but they weren’t stupid. They just liked spiced food, when they could afford it.