Perhaps the biggest problem with negative emotions, such as fear, anger, and disgust, is they can feed back in unexpected ways, especially if the object of the fear is not clear-cut and if the speaker doesn't provide a positive alternative.
It's a bit like starting a fire; you need to know how you're going to control it.
For example, being afraid of germs in general can lead to a crippling fear of touching anything at all, so channelling the fear towards certain circumstances (such as in a hospital or during a viral outbreak) and directing the audience towards alternatives (such as hand-washing) can be more reasonable.