I think that like many of the intellectual problems in contemporary society this arises from a widespread misunderstanding of a philosophical issue. In this case, it leads all the way back to Hume and Kant. The error is in believing that absolute knowledge is knowledge with no properties of any kind...no person who knows it, no method by which it is known, no context within which it is true, no degree of accuracy within which is it true, etc. Of course they can never prove that these kinds of requirements apply (and if they somehow did, they would be making yet another absolute claim in addition to their original one), but that doesn't seem to slow them down at all. That's because this whole approach to thinking is not intended to help us understand the truths of the world, it is designed to let people get away with putting forth false claims without being held accountable for the error.

For example, if I said that the mass of the Sun is greater than the mass of my little finger, some wise ass is bound to assert that it is impossible to know the mass of either one because I don't have the capability to determine exactly how many atoms are in each and that any measure of mass would necessarily be an estimate so that while it is very likely that such an estimate is correct, one can never know absolutely for sure that it is so.

Back in the old days they used to call this "sophistry" and teach kids to spot it and avoid it. Today it is taught as the height of wisdom and sophistication, just as an aesthetic taste for excrement and splatters is taught in art as the true mark of the aesthetic sense. These are just different aspects of the same intellectual problem...in much of academia the pursuit of error, excuse, and evasion has taken the place of the search for the truth.

--Brian