Tell us about the dinosaurs

[Ryft]

Can reason and evidence disprove the existence of invisible pink unicorns?

Only if IPUs are defined in a way subject to reason and evidence.

Why don't you believe in them?

For three principal reasons: nothing requires their existence (predication), other than IPUs themselves; no evidence or compelling reason to believe they exist has ever been presented to me; they are characterized in a manner that defies intelligibility.

If I believed (sincerely) in the existence of IPUs, you could rightfully call me delusional. Can you prove these unicorns are a delusion?

As you told me I could rightly call you delusional, so you must also tell me how I could prove they are a delusion. On the other hand, if I am left to speak for myself, I would say that I have no idea whether or not they are a delusion because I have no idea what your IPU-belief consists of.

Isn't asking to prove that the delusions of the delusional are not true a bit like asking to prove a negative?

Essentially a delusion is a persistent false belief held in the face of strong contradictory evidence. Thus, unless you can demonstrate that some belief is false using strong contradictory evidence, you should not classify it as a delusion—otherwise you put yourself in the position of trying to prove a negative.