That is not such an easy answer. The illusions themselves are just that: illusions. However, in the same manner that I am unable to prevent my illusions from being activated when my eyes are open, I am also unable to create illusions without feeding on the soul in some manner.

If I am purposefully creating my illusions, they are harmless. I can choose to make them as plain or as peaceful as I wish. But, should my blindfold fall away and a person get a glimpse of my eyes before I have time to prepare... well. I suppose you could say all illusionists have a "default" of sorts. Unless I am consciously making an effort to control my illusions, the creature in question would have their worst possible fears reflected at them.