For the most part, milk is pasteurized in modern times because the huge automated factory farm style of milk production often has such terrible conditions for cows that it does indeed result in milk contaminated with salmonella and fecal coliform bacteria. Raw milk does not contain any harmful bacteria unless it has been contaminated after milking. The dairy that I get milk from actually does test each batch of milk before delivery (they put a little of each cows milk together and have a test they do which turns colors if various kind of bacteria and what not are present).

Raw milk does, on the other hand, have beneficial bacteria and enzymes which help you digest the milk much better than pasturized milk. Many people that are "lactose intolerant" can drink raw milk without issues.