Here's why you might lie about it: By claiming you used to be a liberal, you get to claim insider knowledge of what that is like, then make broad generalizations about all liberals. You would also get to present yourself as a thoughtful person who has considered both sides and chosen the superior one.
Using drug addiction for this example, sometimes former addicts make the best counselors because they have been there and can empathize. Sometimes they become condescending pricks who think they're superior for having gotten out, and who look down on others for not having overcome it. The same could be said of people who have abandoned a faith or abandoned atheism, ex-gays (lol), or a variety of people who have changed something in their life. It's pretty obvious you've chosen the latter path, the path of condescension. Ironically, for all that arrogance, it's also evidence of self-loathing. I'm pretty confident that 10 years from now, you'll hate the you you are today.
My last year of undergrad, I TA'd for a professor. After I expressed annoyance about a particular student, the professor laughed and said, "They're just like you were 3 years ago." I realized upon reflection that she was right, and that what I didn't like about the student was how I was reminded of a younger, embarrassing version of myself. I was 22 then, and it marks a significant step in the development of my empathy. So I call you out for your condescension, self-loathing, and lack of empathy at least in part as someone who has been there.
But I take you at your word, unlike how you treat others. It's a pretty crazy stretch that you would go from being liberal to rejecting the Civil Rights Movement of the 1960s. Even among conservatives, there's pretty wide acceptance and admiration for the Civil Rights Movement.