How can one tell if one has thought through their political beliefs? One piece of evidence might be that those beliefs have changed, significantly, from the beliefs you inherited from your parents and ealry environment. Even more so if you can say, because I learned facts X, Y, and Z, this changed my political beliefs.

At the same time, be careful not to confuse beliefs about fact with beliefs about values. I still have much the same political values I had 30 years ago. However I have very different political beliefs than I did then, primarily as a result of learning certain facts about 20th century history.