We have dairy cows these days. Raw milk straight from the cow takes an extremely long time to actually spoil in a dangerous sense. If left out it will sour and eventually separate, while it isn't usually what a person would want to eat it isn't dangerous. It absolutely doesn't go bad in a fridge, we've had jars in the fridge for weeks with absolutely no problem.
3 day old, unrefrigerated pasteurized milk is absolutely dangerous, don't drink it. Pasteurization of milk became commonplace as a solution for shipping milk long distances and storing it in warehouses for days or weeks. If pasteurized and managed properly the flavor won't changed. Raw milk will effectively ferment at room temp as the lactic acid bacteria begins to consume lactose. The byproducts aren't dangerous and are effectively the curds and whey that Little Miss Muffet told us all about, that's just not what you want to find in a jug of milk at the store.