They set out to prove that a phenomenon cannot exist, rather than examining the evidence to reach a conclusion. If one sets out to debunk a phenomenon, then one has reached a conclusion beforehand and therefore cannot examine the evidence before arriving at a conclusion. If you’ve already decided the idea is ludicrous, then you have lost all objectivity before you’ve even begun your investigation. Although these folks liked to call themselves skeptics, I prefer to call them pseudo-skeptics. ~ (Shiel)
In particular, Shiel refers to Joe Nickell's article The Truth Behind Modern Cryptozoological Myths which I commented on here last week.
Thanks to Lesley at The Debris Field for link.