That's like saying you shouldn't be mad at someone who attempted to murder you because they failed. There's a reason we have a crime called "attempted murder". You may find the wikipedia article on "Inchoate offense" interesting, specifically the section on Impossibility[1].

1: http://en.wikipedia.org/wiki/Inchoate_offense#Impossibility

If I learned that a co-worker believed that nuts were invariably fatal to me and gone on to hide some in my food, the nuts would do me no harm but I would still take the whole incident seriously.

I meant "might be real" according to generic-you in that statement. Someone being wrong doesn't make information hazards in general disappear.