What Is Critical Thinking? An Introduction

On my first day of critical thinking class, I'd like to begin by defining critical thinking in terms of the market place of ideas, competing narratives for power and policy, the mythological view of things that creates the conventional assumptions and the deconstructed view that creates subversive views. 

I'd like to give examples of competing narratives in these areas:

compulsory schooling, to develop minds or to indoctrinate the masses into docile sheep?

vaccines, essential safety precaution or medical industry ploy that creates autism and other problems? 

Colombus, the man who "discovered" America or a barbarian. 

Thanksgiving, a time of peaceful exchange between the pilgrims and Indians, or a time of genocide?