Satire, Irony, Voltaire's Candide ...and John Locke's Letter
What is satire? Generally: dead-pan comedy mockingly emulating established power for the purpose of correcting the excesses of that power. Satire generally exaggerates the excess -- attempting to show how absurd that power is if taken to its extreme; in this way, satire implicitly critiques extremes and generally operates as a voice of moderation. Satire normally relies heavily on irony.
What is irony? Generally: inverted logic; the opposite of what was expected.
Why did Enlightenment author's privilege satire and irony?
First, in order for irony to work, the audience needs to understand both logic and the topic being inverted, so irony requires both intelligence or reason and knowledge for it to make sense. The Enlightenment privileges intelligence, reason and knowledge.
Second, Enlightenment principles privilege intelligence, reason and knowledge as the most valid means of building a better society, so it's logical that these are also used to criticize the existing social norms: satire and irony show the audience that the current system doesn't make sense, that is, that it is irrational, illogical, and plain ol' stoopid, etc.
Third, Enlightenment principles privilege increased individual liberty and freedom of speech most obviously when those in power, the current system, is attempting to curtail those liberties and freedoms; in other words, when those in power are likely to jail, banish or imprison those who challenge that power. Because satire doesn't obviously advance an agenda or program of its own -- in contrast to, say, making a speech or delivering a sermon, satire generally only critiques and implies its own agenda/ideas -- it is difficult for those in power to crack down on satire because to do so is to admit that the satire has validity. Satire's criticism is hidden beneath the fact that on the surface it agrees with whatever it is attempting to correct.
Fourth, it's easier to keep an audience's attention if they are laughing than if you are boring them with lectures and sermons.
So, what was Voltaire trying to satirize in the 1750s, what does it have to do with lectures on John Locke, and what does it have to do with me in the 21st Century?
In many ways, The Ballad Of Ricky Bobby mirrors the same satirical thematic (and, actually, some of the plot) elements you'll find in Candide:
http://www.youtube.com/watch?v=zKDC2iBQTYg&mode=related&search=
Other current examples: The Daily Show, The Simpsons, South Park, Team America, The Onion etc.