I think scaremongering is a bit strong. There are plenty of examples, both on these forums and others, where owners haven't used the correct fluid, such as a standard dexron fluid, and their transmissions very quickly started to misbehave.
If T-IV is recommended/mandated then I'd recommend that advise is followed. Obviously a direct equivalent can also be used, such as the OEM Mobil 3309, and owners should do their own research to make sure what they are using is compatible.