The American Heritage Dictionary defines Relativism (the philosophy) as "The doctrine that no ideas or beliefs are universally true but that all are, instead, 'relative' — that is, their validity depends on the circumstances in which they are applied."  This philosophy can be summed up by the notion that there is no absolute (i.e. 'objective') truth.

In a similar way, Postmodernism, which promotes the notion of radical pluralism (i.e. there are many "ways of knowing" and "reality is subject to perspective", etc. etc.), promotes the complimentary notion that truth is something we interpret out of our individual realities rather than something that actually exists. 

These philosophies (in particular) frame our default "modern" worldview - which is what is being taught to students in our (western) public educational systems.  Pragmatically it lends itself to the notion that all religions and cultures are equal in that we cannot know which (if any of them) is right or superior.

Unfortunately, the perceived educational benefits of a postmodernism, relativistic worldview (pluralism, secularism, etc.) come at the expense of critical thinking - which posits that in order to think clearly on a matter, one's knowledge must be informed by and through factual evidence.  In a culture that has convinced itself that truth is unknowable, or that truth is a matter of perspective, knowledge can no longer be informed by factual evidence, because there is no such thing as an actual, objective fact.  All truth is inherently subjective and a matter of perspective, therefore even where evidence supports a claim, the claim may be rejected because our philosophies presuppose that even factual evidence is subject to opinion and perspective. There simply is no room to think critically, because critical thought presumes upon the objectivity of the evidence.

Therefore, if humans are in fact losing the ability to think critically, it probably doesn't spring from recent technological advances, but rather from recent trends in epistemological philosophies. A generation that is so enlightened that it teaches itself that nothing is truly knowable, can hardly escape the conclusion presupposed by its worldview: There is no longer any need for critical thinking since that archaic notion was premised upon a notion our worldview denies.