It's easy to "trap" someone if you act as if the puzzle is explicit when it isn't.
Before responding I will apologize in advance. Not trying to bust your chops, but it is a useful dialog...:
I would suggest that the reason these logical fallacies are so pervasive is two fold: a) we are wired oddly, b) we have a great deal of trouble being self-observant and thus discovering our tendency to commit the fallacy. In this particular case you are trying to blame the way I set up the puzzle. I do not take offense but would suggest you are missing the point:
a) You explicitly asked me to restate (a fair request) and I was completely unambiguous and crystal clear. (yes, in the first iteration I was less clear - but if you asked for restatement presumably you were trying to avoid the very issue you are now claiming)
b) You used as your calculation method an assumption that is always wrong except by shear happenstance (FP+FN=1.0).
c) You are attempting to justify your answer by stating 1 percent incidence is silly. But even with high incidences (try 20%) the answer remains Drug B (the safe drug).
As a general comment on the human condition this inability to be self-observant is at the root of many issues. Psychology is replete with them - from the banal (80 percent of the population thinks of themselves as better than average drivers) to the depressing (almost everyone told of the Milgram Experiment believes that they would not behave in that way - but the vast majority across all cultures did behave that way.)
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