Amanda Marcotte has as good an explanation as any I've seen of the right-wing penchant for self-flattering conversion stories:
[T]he association of Republicanism with bigotry and small-minded stupidity has a lot to do with the allure of the conversion story ... There's a huge amount of psychological energy on the Republican side in trying to distance themselves from their images as small-minded bigots. One strategy is declaring yourself a "libertarian". (Ron Paul clearly not knowing what either a Blackberry or an iPhone is probably was another nail in the coffin for using "libertarian" to try to pass yourself off as a hip Republican.) Calling yourself the Tea Party is a new version of this, though it's definitely of a more populist and less trying-to-be-hip flavor. And then you have the conversion story. If you claim you used to be a Democrat, but then saw the light, you're basically claiming (falsely in many cases) that you actually considered liberal arguments seriously, but decided the President is a secret Muslim anyway.The shorter version is that a youstabee is a person who doesn't want to be seen as a shiftless, mindless clod sitting on the couch issuing demands about taxes and minorities.
What I can say is that with only two exceptions I could name, every hard-boiled "conservative" I know has a conversion story to share, an account of how his former liberalism gave way to his current "conservative" outlook under the harsh glare of experience.
Maybe so, maybe not -- I am not a mind-reader, not even for purposes of this blog post. I used to think my personal interactions and relationships could form a sturdy-enough grounding on which to base far-reaching conclusions about people. I used to be silly that way.