I know I shouldn't take chaff talk too seriously, but the amount of bad science behind stories like that has gotta be frustrating for McD's. People unintentionally dehydrate these thin burgers into essentially jerky, and then make unsubstantiated claims it's because of preservatives. They observe an effect (doesn't rot) and assume a cause.
There's lot of reasons to hate McD's, but this isn't one of them. There's zero preservatives in McD's burgers aside from the salt that is sprinkled on after. This is simply a thin slice of meat dehydrating before mold has time to grow on it. Note that McDonald's Quarter Pounder burgers (same meat but thicker) do readily mold because they're thicker and take longer to dry out.